Heat-sensitive imaging element

ABSTRACT

A heat-sensitive imaging element includes an IR dye, and more particularly a heat-sensitive lithographic printing plate precursor includes the IR dye. A method for making the lithographic printing plate produces a print-out image of high contrast upon exposure to IR-radiation or heating.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/EP2006/063327, filed Jun. 20, 2006.This application claims the benefit of U.S. Provisional Application No.60/694,226, filed Jun. 27, 2005, which is incorporated by referenceherein in its entirety. In addition, this application claims the benefitof European Application No. 05105440.1, filed Jun. 21, 2005, which isalso incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an infrared absorbing dye. The presentinvention relates also to a heat-sensitive imaging element including theIR dye and more particularly, to a heat-sensitive lithographic printingplate precursor including the IR dye. The present invention relates alsoto a method for making a lithographic printing plate whereby a print-outimage of high contrast is formed upon exposure to IR-radiation.

2. Description of the Related Art

Lithographic printing typically involves the use of a so-called printingmaster such as a printing plate which is mounted on a cylinder of arotary printing press. The master carries a lithographic image on itssurface and a print is obtained by applying ink to the image and thentransferring the ink from the master onto a receiver material, which istypically paper. In conventional lithographic printing, ink as well asan aqueous fountain solution (also called dampening liquid) are suppliedto the lithographic image which consists of oleophilic (or hydrophobic,i.e., ink-accepting, water-repelling) areas and hydrophilic (oroleophobic, i.e., water-accepting, ink-repelling) areas. In so-calleddriographic printing, the lithographic image consists of ink-acceptingand ink-abhesive (ink-repelling) areas and during driographic printing,only ink is supplied to the master.

Printing masters are generally obtained by the image-wise exposure andprocessing of an imaging material called a plate precursor. A typicalpositive-working plate precursor includes a hydrophilic support and anoleophilic coating which is not readily soluble in an aqueous alkalinedeveloper in the non-exposed state and becomes soluble in the developerafter exposure to radiation. In addition to the well knownphotosensitive imaging materials which are suitable for UV contactexposure through a film mask (the so-called pre-sensitized plates),heat-sensitive printing plate precursors have also become very popular.Such thermal materials offer the advantage of daylight stability and areespecially used in the so-called computer-to-plate method (CtP) whereinthe plate precursor is directly exposed, i.e., without the use of a filmmask. The material is exposed to heat or to infrared radiation and thegenerated heat triggers a (physico-)chemical process, such as ablation,polymerization, insolubilization by cross-linking of a polymer or byparticle coagulation of a thermoplastic polymer latex, andsolubilization by the destruction of intermolecular interactions or byincreasing the penetrability of a development barrier layer.

It is important in the printing plate preparation work that the exposedplate precursor shows a visible image even before being developed ifnecessary, i.e., a print-out image. This enables the end-user toestablish immediately whether or not the precursor is already exposed tolight, to inspect images on the printing plate, and to distinguish theplate as to which color of ink should be applied. In such a work flow,the exposed printing plate is developed later in a separate developingstep or in an on-press processing step, or is further used in theprinting process without the need of a developing step.

On-press processing is disclosed in EP 770 494, wherein the plate ismounted on the press and the coating layer is developed by interactionwith the fountain solution and ink that are supplied to the cylinderduring the press run. During the first runs of the press, thenon-exposed areas (for a negative-working precursor) are removed fromthe support and thereby define the non-printing areas of the plate.Since development of the plate is not carried out before starting theprinting process, a previous inspection and discrimination of the plateis not possible unless there is formed a print-out image.

Several methods for forming a print-out image are known for photopolymersystems such as disclosed in U.S. Pat. No. 3,359,109; U.S. Pat. No.3,042,515; U.S. Pat. No. 4,258,123; U.S. Pat. No. 4,139,390; U.S. Pat.No. 5,141,839; U.S. Pat. No. 5,141,842; U.S. Pat. No. 4,232,106; U.S.Pat. No. 4,425,424; U.S. Pat. No. 5,030,548; U.S. Pat. No. 4,598,036; EP0 434 968; WO 96/35143; and U.S. 2003/68575. In these materials thephoto initiating system is a reacting component which induces formationof the print-out image upon exposure and therefore the performance ofthe lithographic differentiation process is reduced.

The formation of a print-out image is also known for heat-sensitivelithographic printing plates. The plates are usually image-wise exposedby an IR-laser and are consequently sensitive to IR-radiation. Theseprinting plate precursors include, beside an IR dye as the light-to-heatconversion compound, also a dye which absorbs in the visible lightwavelength range and which undergoes a color change upon heating. Thiscolor change can be obtained with a heat-decomposable dye which isbleached upon heating such as disclosed in DD 213 530, EP 897 134, EP 0925 916, WO 96/35143, and EP 1 300 241. The color change can also be theresult of a shift of the absorption maximum of the visible dye byheating as disclosed in EP 1 502 736 and EP 0 419 095.

EP 1 508 440 discloses a lithographic printing process wherein aprinting plate precursor includes an IR-dye and a dye-precursor, thedye-precursor having no substantial absorption in the visible lightwavelength range. Upon image-wise exposure with IR-light, a dye isformed from the dye-precursor, the dye having an absorption in thevisible light wavelength range.

EP 1 428 676 describes print-out formation, upon IR-light exposure, withdye-precursors (coloration) or with dyes that undergo discoloration byacid or radicals, formed during IR-light exposure.

The heat-sensitive lithographic printing plate precursors of EP 0 925916 and EP 1 428 676 use an IR dye which act to convert IR-radiation toheat and which changes in color due to the IR-radiation. In these priorart materials, the IR dyes exhibit, beside strong absorption in the IRwavelength range, also side-absorption in the visible wavelength range.Due to IR-exposure, the IR dye decomposes and a print-out image isbuilt-up by the reduction of this side-absorption in the visiblewavelength range. A problem of these prior art materials is the lowcontrast of the print-out images.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide an infrared absorbing dye as definedbelow, the infrared absorbing dye preferably being capable of forming acolor upon IR exposure or heating.

In another preferred embodiment of the present invention, aheat-sensitive imaging element is disclosed including the IR dyes havinga structure as defined below.

In another preferred embodiment of the present invention, aheat-sensitive lithographic printing plate precursor is disclosedincluding the IR dyes having a structure as defined below.

In another preferred embodiment of the present invention, a method isdisclosed wherein a lithographic printing plate precursor, including theIR dyes having a structure as defined below, is image-wise exposed to IRlight or heat, optionally followed by a development step.

In another preferred embodiment, a method is disclosed wherein theimage-wise exposed heat-sensitive lithographic printing plate precursor,having a print-out image, is developed in an on-press processing step.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments thereof with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the absorption spectrum of a comparative printing plateprecursor at different exposure energies: curves 1 to 5 respectively for0, 125, 200, 275, and 350 mJ/cm², curve 6 for the base line for thealuminum support, wherein A represents the absorption at each wavelength(nm).

FIG. 2 shows the absorption spectrum of a printing plate precursoraccording to a preferred embodiment of the present invention atdifferent exposure energies: curves 1 to 5 respectively for 0, 125, 200,275, and 350 mJ/cm², curve 6 for the base line for the aluminum support,wherein A represents the absorption at each wavelength (nm).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The infrared absorbing dye, hereinafter also called IR dye, according topreferred embodiments of the present invention has a structure accordingto Formula I:

wherein

-   ⁺Y¹=is represented by one of the following structures:

-   T²—is represented by one of the following structures:

-   n is 0, 1, 2, or 3;-   each of p and q is 0, 1, or 2;-   R¹ and R² are independently an optionally substituted hydrocarbon    group, or wherein two of the R¹, R², R^(d), or R^(a) groups together    include the necessary atoms to form a cyclic structure;-   characterized in that:-   at least one of the R^(d) groups is selected from the list    consisting of:-   —(N═CR¹⁷)_(a)—NR⁵—CO—R⁴,-   —(N═CR¹⁷)_(b)—NR⁵—SO₂—R⁶,-   —(N═CR¹⁷)_(c)—NR¹¹—SO—R¹²,-   —SO₂—NR¹⁵R¹⁶ and-   —S—CH₂—CR⁷(H)_(1-d)(R⁸)_(d)—NR⁹—COOR¹⁸;-   a, b, c, and d independently are 0 or 1;-   R¹⁷ is a hydrogen atom, an optionally substituted aliphatic    hydrocarbon group, or an optionally substituted (hetero)aryl group,    or wherein R¹⁷ and R⁵, R¹⁷ and R¹¹ together include the necessary    atoms to form a cyclic structure;-   R⁴ is —OR¹⁰, —NR¹³R¹⁴, or —CF₃;-   wherein R¹⁰ is an optionally substituted (hetero)aryl group or an    optionally branched aliphatic hydrocarbon group;-   R¹³ and R¹⁴ independently are a hydrogen atom, an optionally    substituted aliphatic hydrocarbon group, or an optionally    substituted (hetero)aryl group, or wherein R¹³ and R¹⁴ together    include the necessary atoms to form a cyclic structure;-   R⁶ is an optionally substituted aliphatic hydrocarbon group or an    optionally substituted (hetero)aryl group, —OR¹⁰, —NR¹³R¹⁴, or —CF₃;-   R⁵ is a hydrogen atom, an optionally substituted aliphatic    hydrocarbon group, a SO₃ ⁻ group, a —COOR¹⁸ group, or an optionally    substituted (hetero)aryl group, or wherein R⁵ together with at least    one of R¹⁰, R¹³, and R¹⁴ include the necessary atoms to form a    cyclic structure;-   R¹¹, R¹⁵, and R¹⁶ are independently a hydrogen atom, an optionally    substituted aliphatic hydrocarbon group, or an optionally    substituted (hetero)aryl group, or wherein R¹⁵ and R¹⁶ together    include the necessary atoms to form a cyclic structure;-   R¹² is an optionally substituted aliphatic hydrocarbon group or an    optionally substituted (hetero)aryl group;-   R⁷ and R⁹ independently are a hydrogen atom or an optionally    substituted aliphatic hydrocarbon group;-   R⁸ is —COO⁻ or —COOR^(8′), wherein R^(8′) is a hydrogen atom, an    alkali metal cation, an ammonium ion, or a mono-, di-, tri- or    tetra-alkyl ammonium ion;-   R¹⁸ is an optionally substituted (hetero)aryl group or an    alpha-branched aliphatic hydrocarbon group; and-   the R^(a) and other R^(d) groups are independently represented by a    group selected from the list consisting of a hydrogen atom, a    halogen atom, —R^(e), —OR^(f), —SR^(g), and —NR^(u)R^(v), wherein    R^(e), R^(f), R^(g), R^(u), and R^(v) independently are an    optionally substituted aliphatic hydrocarbon group or an optionally    substituted (hetero)aryl group; and-   one or more counter ions in order to obtain an electrically neutral    molecule.

The IR dye of preferred embodiments of the present invention ispreferably capable of forming a color upon exposure to IR-radiation orheat. The coloration may be the result of a chemical transformation uponexposure to IR-light or heat of at least one R^(d) group, selected fromthe list consisting of:

-   —(N═CR¹⁷)_(a)—NR⁵—CO—R⁴,-   —(N═CR¹⁷)_(b)—NR⁵—SO₂—R⁶,-   —(N=CR¹⁷)_(c)—NR¹¹—SO—R¹²,-   —SO₂—NR¹⁵R¹⁶, and-   —S—CH₂—CR⁷(H)_(1-d)(R⁸)_(d)—NR⁹—COOR¹⁸;    wherein the meaning of a, b, c, d, R¹⁷, R⁵, R⁴, R⁶, R¹¹, R¹², R¹⁵,    R¹⁶, R⁷, R⁸, R⁹, and R¹⁸ is the same as described above and wherein    the chemical transformation results in an increased light absorption    in the visual wavelength range, namely between 400 nm and 700 nm.    Color formation by the chemical transformation of at least one of    these R^(d) groups may be due to the transformation of the R^(d)    group into a group which is a stronger electron-donor than the R^(d)    group.

Coloration of the IR dye may also be the result a chemicaltransformation upon exposure to IR-radiation or heat of a R^(a) groupinto a group which is a stronger electron-acceptor than the R^(a) group.

The IR dyes described above can be used in imaging elements, e.g.,lithographic printing plate precursors, to form a print out image uponexposure to IR light or heat. This is clearly illustrated in FIG. 2wherein a printing plate precursor including an IR-dye of a preferredembodiment of the present invention shows a build-up of the absorptionin the visual range while the absorption in the IR-wavelength rangedecreases by IR-radiation. The formation of this print-out image isclearly different from a bleaching process as illustrated in FIG. 1 fora comparative IR-dye whereby the IR-dye decomposition produces only aslight decrease of the absorption in the visible spectrum, namelybetween about 600 nm and 700 nm. As there is no substantial increase ofthe absorption in the wavelength range between 400 nm and about 600 nm,no build-up of the optical density in the visual part of the spectrum isobserved. The IR dyes of preferred embodiments of the present inventionmay exhibit an increase of the optical density in the visual wavelengthrange and, as a result, the contrast of the print-out image may beimproved compared to the IR-dyes whereby only bleaching takes place.

According to another preferred embodiment of the present invention, theIR-dye has the structure of one of the following Formulae II, III, orIV:

wherein

-   Ar¹, Ar², and Ar³ are independently an optionally substituted    aromatic hydrocarbon group or an aromatic hydrocarbon group with an    annulated benzene ring which is optionally substituted;-   W¹ and W² are independently a sulphur atom or a —CM¹⁰M¹¹ group,    wherein M¹⁰ and M¹¹ are independently an optionally substituted    aliphatic hydrocarbon group or an optionally substituted    (hetero)aryl group, or wherein M¹⁰ and M¹¹ together include the    necessary atoms to form a cyclic structure, preferably a 5- or    6-membered ring;-   M¹ and M² are independently a hydrogen atom, an optionally    substituted aliphatic hydrocarbon group, or wherein M¹ and M²    together include the necessary atoms to form an optionally    substituted cyclic structure, preferably a 5- or 6-membered ring,    more preferably a 5-membered ring, most preferably a 5-membered ring    having a cyclic structure of 5 carbon atoms;-   M³ and M⁴ are independently an optionally substituted aliphatic    hydrocarbon group;-   M⁵, M⁶, M⁷, M⁸, M¹⁶, and M¹⁷ are independently a hydrogen atom, a    halogen atom, or an optionally substituted aliphatic hydrocarbon    group;-   W³ is a sulphur atom or a —CA³═CA⁴— group;-   M¹² and M¹³ are independently an optionally substituted aliphatic    hydrocarbon group or an optionally substituted (hetero)aryl group,    or wherein two of the M¹², M¹³, A², or A⁴ together include the    necessary atoms to form at least one cyclic structure, preferably a    5- or 6-membered ring;-   W⁴ is a sulphur atom or a —CA⁷═CA⁸— group;-   A¹ to A⁸ are independently a hydrogen atom, a halogen atom, an    optionally substituted aliphatic hydrocarbon group, or an optionally    substituted (hetero)aryl group, or wherein each of A¹ and A², A³ and    A⁴, A⁵ and A⁶, or A⁷ and A⁸, together include the necessary atoms to    form a cyclic structure, preferably a 5- or 6-membered ring;-   M¹⁴ and M¹⁵ are independently an optionally substituted aliphatic    hydrocarbon group or an optionally substituted (hetero)aryl group,    or wherein two of the M¹⁴, M¹⁵, A⁵, or A⁷ together include the    necessary atoms to form at least one cyclic structure, preferably a    5- or 6-membered ring, and-   M⁹ is a R^(d) group selected from the list consisting of:-   —(N═CR¹⁷)_(a)—NR⁵—CO—R⁴,-   —(N═CR¹⁷)_(b)—NR⁵—SO₂—R⁶,-   —(N═CR¹⁷)_(c)—NR¹¹—SO—R¹²,-   —SO₂—NR¹⁵R¹⁶, and-   —S—CH₂—CR⁷(H)_(1-d)(R⁸)_(d)—NR⁹—COOR¹⁸,    wherein the meaning of a, b, c, d, R¹⁷, R⁵, R⁴, R⁶, R¹¹, R¹², R¹⁵,    R¹⁶, R⁷, R⁸, R⁹, and R¹⁸ is the same as described above; and one or    more counter ions in order to obtain an electrically neutral    molecule.

The dye can be a neutral, an anionic, or a cationic dye depending on thetype of the substituting groups and the number of each of thesubstituting groups. In a preferred embodiment, the dye of Formula II,III, or IV has at least one anionic or acid group, selected from thelist consisting of —CO₂H, —CONHSO₂R^(h), —SO₂NHCOR^(i), —SO₂NHSO₂R^(j) ,—PO₃H₂, —OPO₃H₂, —OSO₃H , —S—SO₃H, or —SO₃H groups or theircorresponding salts, wherein R^(h), R^(i), and R^(j) are independentlyan aryl or an alkyl group, preferably a methyl group, and wherein thesalts are preferably alkali metal salts or ammonium salts, includingmono- or di- or tri- or tetra-alkyl ammonium salts. These anionic oracid groups may be present on the aromatic hydrocarbon group or theannulated benzene ring of Ar¹, Ar², or Ar³, or on the aliphatichydrocarbon group of M³, M⁴, or M¹² to M¹⁵, or on the (hetero)aryl groupof M¹² to M¹⁵. Other substituting groups can be selected from a halogenatom, a cyano group, a sulphone group, a carbonyl group, or a carboxylicester group.

In another preferred embodiment, each of the aliphatic hydrocarbongroups of M³, M⁴, or M¹² to M¹⁵ is terminally substituted with at leastone of these groups, more preferably with —CO₂H, —CONHSO₂-Me,—SO₂NHCO-Me, —SO₂NHSO₂-Me, —PO₃H₂, or —SO₃H groups or theircorresponding salt, wherein Me represents a methyl group.

According to another preferred embodiment of the present invention, theIR-dye has the structure of one of the following Formulae II-10, II-11,II-20, II-21, III-10, III-11, III-20, III-21, IV-10, IV-11, IV-20, orIV-21:

wherein

-   Q is O, S, —CR^(s)R^(t), or —COOR¹¹ wherein R^(s), R^(t), and R^(u)    are independently a hydrogen atom or an alkyl group and the other    groups have the same meaning as defined in Formula II, III, and IV.

According to another preferred embodiment of the present invention, theIR-dye has the structure of one of the following Formulae V-a, V-b, V-c,or V-d:

wherein

-   M⁺=Li⁺, Na⁺, K⁺, NH₄ ⁺, R′R″R′″NH⁺ wherein R′, R″, R′″ are    independently a H atom, an optional substituted alkyl or aryl group;-   X=halogen, sulphonate, perfluorosulphonate, or arylsulphonate; and-   R³, R^(3′) are methyl or ethyl.

The IR-dyes mentioned above may also be coupled to each other or toother IR absorbing dyes as to form IR dye dimers or oligomers. Besides acovalent coupling between two or more IR dyes, supra-molecularcompounds, including two or more IR dyes, may also be formed by ionicinteractions. Dimers, consisting of two different IR dyes, may be formedfor example by an interaction between a cationic and an anionic IR dye,as described in, e.g., WO 2004/069938 and EP 1 466 728. Infrared dyesmay also be ionically bond to a polymer as, e.g., described in EP 1 582346 wherein IR dyes, including two to four sulphonate groups aretonically bonded to a polymer including covalently attached ammonium,phosphonium, and sulphonium groups.

Supra-molecular compounds, including two or more IR dyes, may also beformed by hydrogen bonding or dipole-dipole interaction.

Suitable examples of IR-dyes according to preferred embodiments of thepresent invention are:

According to another preferred embodiment of the present invention, aheat-sensitive lithographic printing plate precursor is provided whichincludes (i) a support having a hydrophilic surface or which is providedwith a hydrophilic layer; and (ii) on the support, a coating includingan IR dye of Formula I, II, III, IV, V-a, V-b, V-c, or V-d. The coatingis hereinafter also referred to as a “heat-sensitive coating”.

The heat-sensitive coating of preferred embodiments of the presentinvention may include at least one or more layers such as an imagerecording layer, a top layer, an intermediate layer between the supportand the image-recording layer, and/or an intermediate layer between thetop layer and the image-recording layer.

The IR dye of various preferred embodiments of the present invention maybe present in at least one layer of the heat-sensitive coating, e.g., inan image recording layer, in a top layer, in an intermediate layerbetween the support and the image-recording layer, or in an intermediatelayer between the top layer and the image-recording layer, preferably inan image-forming layer and/or in a top layer.

The concentration of the IR-dye in the heat-sensitive coating depends onthe type of the heat-sensitive coating. Heat-sensitive coatings whichinclude a photopolymerizable composition, thermoplastic polymerparticles, microcapsules, a switchable polymer, or an alkaline solublepolymer in combination with a solubility inhibiting compound, usuallycontain an IR dye in a concentration ranging between 0.25% and 50% byweight, preferably between 0.5% and 30% by weight, more preferablybetween 0.7% and 20% by weight relative to the coating as a whole.Heat-sensitive coatings which ablate under the influence of IR-radiationor heating may contain higher concentrations of IR-dye, preferablybetween 50% and 100% by weight, more preferably between 75% and 100% byweight relative to the coating as a whole.

The heat-sensitive coating may further include other infrared absorbingcompounds, such as IR-cyanine dyes, IR-merocyanine dyes, IR-methinedyes, IR-naphthoquinone dyes or IR-squarylium dyes, IR-cyanine dyeshaving two indolenine groups, or anionic IR-cyanine dyes having twosulphonic acids or carboxylic acid groups.

Compounds, in the prior art known as photo-initiators orphoto-co-initiators, may enhance the visual contrast, obtained with theIR dyes according to preferred embodiments of the present invention, byfacilitating the transformation reaction of the R^(d) groups, mentionedabove, upon IR exposure.

For example, borates are known to initiate or co-initiatephoto-polymerization reactions. See, e.g., WO 92/13900, EP-A 0 483 648,and EP-A 0 353 030, DE 19 648 282, DE 19 648 313, and ResearchDisclosure, Aug. 10, 1997, pages 493-495. Borates that may enhance theobtained contrast according to preferred embodiments of the presentinvention are represented according to Formula VI.

wherein R_(b) ¹, R_(b) ², R_(b) ³, and R_(b) ⁴ are independently anoptionally substituted aliphatic hydrocarbon group, an optionallysubstituted (hetero)aryl group, a halogen atom and M⁺ is an alkali metalcation such as, e.g., Li⁺, Na⁺, K⁺, an optional substituted ammonium ionaccording to Formula VII. M⁺ may also be a cationic IR dye, moreparticulary a cationic IR dye according to preferred embodiments of thepresent invention.

The borate compounds described in EP-A 1 467 250 (paragraph [0028] onpage 6 to paragraph [0035] on page 12) may also be used as contrastenhancing compounds.

Other initiators or co-initiators, as for example those described inEP-A 1 449 653 and EP-A 1 467 250, may also influence the transformationreaction of the R^(d) groups of the IR dyes according to preferredembodiments of the present invention. These initiators may be used incombination with the borate initiators mentioned above.

Ammonium compounds according to Formula VII may also facilitate thetransformation reaction of the R^(d) groups mentioned above.

wherein R_(n) ¹, R_(n) ² and R_(n) ³ are independently an optionallysubstituted aliphatic hydrocarbon group, an optionally substituted(hetero)aryl group, or a halogen atom. X⁻ is a halide, a sulphonategroup, a carboxylate group, or a phosphate or phosphonate group. X⁻ mayalso be an anionic IR dye, more particulary an anionic IR dye accordingto preferred embodiments of the present invention. X⁻ may also be apolymeric compound such as, e.g., partly deprotonated polyacrylic acidor poly (meth)acrylic acid. Poly (meth)acrylic acid may also enhance theobtained contrast, especially in a photopolymerizable composition.

Exposure of the printing plate precursors with ambient daylight, or withsome kind of safelight used while providing the printing plateprecursor, may deterioate the IR dye used, resulting in a decreased IRabsorption and therefore a decreases sensitivity of the precursor. Theaddition of carboxylic acid compounds, especially those described inEP-A 1 467 250 (pages 4 to 6), e.g., phenyl-NH—CH₂—COOH, may improve thedaylight stability of printing plate precursor including IR dyesaccording to preferred embodiments of the present invention.

The daylight stability of the printing plate precursors according topreferred embodiments of the present invention may also be improved byusing the compounds described in EP-A 1 607 233 (paragraph [0038] onpage 5 to paragraph [0063] on page 18). Compounds, known as fragmentableelectron donors, as described in EP-A 1 300 726 and Journal of AmericanChemical Society, 2000, 122, 48, pages 11934-11943, may also improve thedaylight stability of the IR dyes.

The heat-sensitive coating may also further contain other ingredientssuch as additional binders, development inhibitors, or accelerators.

The printing plate precursors used in preferred embodiments of thepresent invention are exposed to infrared radiation, e.g., by aninfrared laser. Preferably, a laser emitting near infrared light havinga wavelength in the range from about 700 nm to about 1500 nm is used,e.g., a semiconductor laser diode, a Nd:YAG, or a Nd:YLF laser. Therequired laser power depends on the sensitivity of the image recordinglayer, the pixel dwell time of the laser beam, which is determined bythe spot diameter (typical value of modern plate-setters at 1/e² ofmaximum intensity: 10-25 μm), the scan speed and the resolution of theexposure apparatus (i.e., the number of addressable pixels per unit oflinear distance, often expressed in dots per inch or dpi; typical value:1000-4000 dpi). Two types of laser-exposure apparatuses are commonlyused: internal (ITD) and external drum (XTD) plate-setters. ITDplate-setters for thermal plates are typically characterized by a veryhigh scan speed up to 500 m/sec and may require a laser power of severalWatts. XTD plate-setters for thermal plates having a typical laser powerfrom about 200 mW to about 1 W operate at a lower scan speed, e.g., from0.1 m/sec to 10 m/sec.

In the development step which may be optionally present, the non-exposedareas of the image-recording layer are removed without essentiallyremoving the exposed areas, i.e., without affecting the exposed areas toan extent that renders the ink-acceptance of the exposed areasunacceptable. The non-exposed areas of the image-recording layer may beremoved by supplying a developing solution. The developing solution maybe water, an aqueous solution, a gum solution, or an aqueous alkalinesolution. The development may be combined with mechanical rubbing, e.g.,by a rotating brush. The developing solution can be applied to theplate, e.g., by rubbing in with an impregnated pad, by dipping,(spin-)coating, spraying, pouring-on, either by hand or in an automaticprocessing apparatus.

In another preferred embodiment of the present invention, the image-wiseexposed printing plate precursor may also be developed by mounting it ona print cylinder of a printing press and supplying an aqueous dampeningliquid and/or ink to the surface of the plate while rotating the printcylinder. This developing step is also called “on-press developing” or“on-press processing”.

According to another preferred embodiment of the present invention, amethod for making a lithographic printing plate without wet processingis disclosed including the steps of (i) providing the heat-sensitivelithographic printing plate precursor, and (ii) image-wise exposing theprecursor to IR-radiation or heat thereby inducing the transformation ofthe IR dye and forming a print-out image. In a preferred embodiment ofthis method, the energy density in the image-wise exposing step is atmost 300 mJ/cm², preferably at most 250 mJ/cm², more preferably at most200 mJ/cm², most preferably at most 175 mJ/cm².

According to another preferred embodiment of the present invention, amethod for making a lithographic printing plate includes the steps of(i) providing the heat-sensitive lithographic printing plate precursor,(ii) image-wise exposing the precursor to IR-radiation or heat therebyinducing the transformation of the IR dye and forming a print-out image,and (iii) developing the image-wise exposed precursor.

The developing solution used in this developing step may be water, anaqueous solution, a gum solution, or an aqueous alkaline solution. In apreferred embodiment of this method, the energy density in theimage-wise exposing step is at most 300 mJ/cm², preferably at most 250mJ/cm², more preferably at most 200 mJ/cm², most preferably at most 175mJ/cm².

In another preferred embodiment of the present invention, the developingstep is preferably carried out by mounting the image-wise exposedprecursor on a printing press and developing the precursor in anon-press developing step. In this on-press developing step, fountainsolution and ink are supplied to the precursor while rotating the plateon the press, resulting in a dissolution of the coating on thenon-printing areas of the precursor. In a preferred embodiment of thismethod, the energy density in the image-wise exposing step is at most300 mJ/cm², preferably at most 250 mJ/cm², more preferably at most 200mJ/cm², most preferably at most 175 mJ/cm².

In accordance with a more preferred embodiment of the present invention,the IR dye is substituted with the anionic or acid groups as definedabove. This is especially advantageous when the image-wise exposedprecursor is developed with water, an aqueous solution, or a gumsolution, and also when the image-wise exposed precursor is developed inan on-press developing step with a fountain solution, in order tominimize the risk of dye stain.

In these systems wherein the printing plate precursor after image-wiseexposure is processed with a developing solution, the heat-sensitivecoating usually includes an additional contrasting dye. Afterprocessing, the coating including this contrasting dye substantiallyremains on the plate only in the printing areas and is removed from theplate on the non-imaging areas, resulting in a visual contrast afterprocessing. According to preferred embodiments of the present invention,the IR dyes may have an additional advantage of forming a good, or evenbetter, contrast after processing, without the addition of such acontrasting dye or by reducing the amount of contrasting dye. Thisomission or reducing of such a contrasting dye can have a still furtheradvantage in improving the clean-out in the non-printing area of theprinting plate. During the wet processing, an undesirable adsorption ofthe contrasting dye on the hydrophilic surface of the support can occurresulting in a reduced hydrophilicity of the support in the non-printingareas and resulting in an increased tendency of toning. These twoadvantages are demonstrated in the Examples.

The support of the printing plate precursor may be a sheet-like materialsuch as a plate or it may be a cylindrical element such as a sleevewhich can be slid around a print cylinder of a printing press.Preferably, the support is a metal support such as aluminum or stainlesssteel.

A particularly preferred lithographic support is an electrochemicallygrained and anodized aluminum support. Graining and anodizing ofaluminum supports is well known. The grained aluminum support used inthe material is preferably an electrochemically grained support. Theacid used for graining can be, e.g., nitric acid or sulphuric acid. Theacid used for graining preferably includes hydrogen chloride. Alsomixtures of, e.g., hydrogen chloride and acetic acid can be used. Therelationship between electrochemical graining and anodizing parameterssuch as electrode voltage, nature, and concentration of the acidelectrolyte or power consumption on the one hand and the obtainedlithographic quality in terms of Ra and anodic weight (g/m² of Al₂O₃formed on the aluminum surface) on the other hand is well known. Moredetails about the relationship between various production parameters andR^(a) or anodic weight can be found in, e.g., the article “Management ofChange in the Aluminium Printing Industry” by F. R. Mayers, published inthe ATB Metallurgie Journal, Volume 42 No. 1-2 (2002), page 69.

The anodized aluminum support may be subject to a so-called post-anodictreatment to improve the hydrophilic properties of its surface. Forexample, the aluminum support may be silicated by treating its surfacewith a sodium silicate solution at an elevated temperature, e.g., 95° C.Alternatively, a phosphate treatment may be applied which involvestreating the aluminum oxide surface with a phosphate solution that mayfurther contain an inorganic fluoride. Further, the aluminum oxidesurface may be rinsed with a citric acid or citrate solution. Thistreatment may be carried out at room temperature or may be carried outat a slightly elevated temperature of about 30° C. to 50° C. A furtherinteresting treatment involves rinsing the aluminum oxide surface with abicarbonate solution. Still further, the aluminum oxide surface may betreated with polyvinylphosphonic acid, polyvinylmethylphosphonic acid,phosphoric acid esters of polyvinyl alcohol, polyvinylsulphonic acid,polyvinylbenzenesulphonic acid, sulphuric acid esters of polyvinylalcohol, and acetals of polyvinyl alcohols formed by reaction with asulphonated aliphatic aldehyde.

Another useful post-anodic treatment may be carried out with a solutionof polyacrylic acid or a polymer including at least 30 mol % of acrylicacid monomeric units, e.g., GLASCOL E15, a polyacrylic acid,commercially available from ALLIED COLLOIDS.

The support can also be a flexible support, which may be provided with ahydrophilic layer, hereinafter called ‘base layer’. The flexible supportis, e.g., paper, plastic film, or aluminum. Preferred examples ofplastic film are polyethylene terephthalate film, polyethylenenaphthalate film, cellulose acetate film, polystyrene film,polycarbonate film, etc. The plastic film support may be opaque ortransparent.

The base layer is preferably a cross-linked hydrophilic layer obtainedfrom a hydrophilic binder cross-linked with a hardening agent such asformaldehyde, glyoxal, polyisocyanate, or a hydrolyzedtetra-alkylorthosilicate. The latter is particularly preferred. Thethickness of the hydrophilic base layer may vary in the range of 0.2 μmto 25 μm and is preferably 1 μm to 10 μm. More details of preferredembodiments of the base layer can be found in, e.g., EP-A 1 025 992.

In a preferred embodiment, the heat-sensitive coating may includehydrophobic thermoplastic polymer particles dispersed in a hydrophilicbinder.

In this type image-recording layer, due to the heat generated during theexposure step, the hydrophobic thermoplastic polymer particles fuse orcoagulate so as to form a hydrophobic phase which corresponds to theprinting areas of the printing plate. Coagulation may result fromheat-induced coalescence, softening or melting of the thermoplasticpolymer particles. There is no specific upper limit to the coagulationtemperature of the thermoplastic hydrophobic polymer particles, howeverthe temperature should be sufficiently below the decompositiontemperature of the polymer particles. Preferably the coagulationtemperature is at least 10° C. below the temperature at which thedecomposition of the polymer particles occurs. The coagulationtemperature is preferably higher than 50° C., more preferably above 100°C.

In the development step, the non-exposed areas of the image-recordinglayer are removed by supplying a developing solution without essentiallyremoving the exposed areas, i.e., without affecting the exposed areas toan extent that renders the ink-acceptance of the exposed areasunacceptable. The developing solution may be water, an aqueous solution,or an aqueous alkaline solution. The development by supplying adeveloping solution may be combined with mechanical rubbing, e.g., by arotating brush. The developing solution can be applied to the plate,e.g., by rubbing in with an impregnated pad, by dipping, (spin-)coating,spraying, pouring-on, either by hand or in an automatic processingapparatus. The image-wise exposed printing plate precursor may also bedeveloped in an on-press processing by mounting it on a print cylinderof a printing press and supplying an aqueous dampening liquid and/or inkto the surface of the plate while rotating the print cylinder.

Specific examples of suitable hydrophobic thermoplastic polymers are,e.g., polyethylene, poly(vinyl chloride), poly(methyl(meth)acrylate),poly(ethyl(meth)acrylate), poly(vinylidene chloride),poly(meth)acrylonitrile, poly(vinyl carbazole), polystyrene orcopolymers thereof. Polystyrene and poly(meth)acrylonitrile or theirderivatives are highly preferred embodiments. According to suchpreferred embodiments, the thermoplastic polymer includes at least 50wt. % of polystyrene, and more preferably at least 60 wt. % ofpolystyrene. In order to obtain sufficient resistivity towards organicchemicals, such as the hydrocarbons used in plate cleaners, thethermoplastic polymer preferably includes at least 5 wt. %, morepreferably at least 30 wt. % of nitrogen containing monomeric units orof units which correspond to monomers that are characterized by asolubility parameter larger than 20, such as (meth)acrylonitrile.Suitable examples of such nitrogen containing monomeric units aredisclosed in EP-A 1 219 416.

According to a highly preferred embodiment, the thermoplastic polymer isa copolymer consisting of styrene and acrylonitrile units in a weightratio between 1:1 and 5:1 (styrene:acrylonitrile), e.g., in a 2:1 ratio.

The weight average molecular weight of the thermoplastic polymerparticles may range from 5,000 to 1,000,000 g/mol. The hydrophobicparticles preferably have a number average particle diameter below 200nm, more preferably between 10 nm and 100 nm, most preferably between 20nm and 63 nm. The amount of hydrophobic thermoplastic polymer particlescontained in the image-recording layer is preferably at least 20 wt. %,more preferably at least 70 wt. % and most preferably between 70 wt. %and 85 wt. %.

The hydrophobic thermoplastic polymer particles may be present as adispersion in an aqueous coating liquid of the image-recording layer andmay be prepared by the methods disclosed in U.S. Pat. No. 3,476,937.Another method especially suitable for preparing an aqueous dispersionof the thermoplastic polymer particles includes dissolving thehydrophobic thermoplastic polymer in an organic water immisciblesolvent, dispersing the thus obtained solution in water or in an aqueousmedium, and removing the organic solvent by evaporation.

The image recording layer preferably further includes a hydrophilicbinder, e.g., homopolymers and copolymers of vinyl alcohol, acrylamide,methylol acrylamide, methylol methacrylamide, acrylic acid, methacrylicacid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleicanhydride/vinylmethylether copolymers. The hydrophilicity of the(co)polymer or (co)polymer mixture used is preferably the same as orhigher than the hydrophilicity of polyvinyl acetate hydrolyzed to atleast an extent of 60 percent by weight, preferably 80 percent byweight.

In another preferred embodiment, the heat-sensitive coating may alsoinclude a photopolymer or a photopolymerizable composition.

In this type of image-recording layer, upon exposure to IR light orheat, the photopolymer or photopolymerizable composition is hardened, soas to form a hydrophobic phase which corresponds to the printing areasof the printing plate. Here, “hardened” means that the coating becomesinsoluble or non-dispersible for the developer and may be achievedthrough polymerization and/or crosslinking of the photosensitivecoating, optionally followed by a heating step to enhance or to speed-upthe polymerization and/or crosslinking reaction. In this optionalheating step, hereinafter also referred to as “pre-heat”, the plateprecursor is heated, preferably at a temperature of about 80° C. to 150°C. and preferably during a dwell time of about 5 seconds to 1 minute.

The photopolymerizable coating provided on the support includes apolymerizable monomer or oligomer and an initiator capable of hardeningthe monomer or oligomer and, optionally, a sensitizer capable ofabsorbing light used in the image-wise exposing step.

The coating thickness of the photopolymerizable coating is preferablybetween 0.1 g/m² and 4.0 g/m², more preferably between 0.4 g/m² and 2.0g/m².

In a preferred embodiment, the polymerizable monomer or oligomer may bea monomer or oligomer including at least one epoxy or vinyl etherfunctional group and the initiator may be a Bronsted acid generatorcapable of generating free acid, optionally in the presence of asensitizer, upon exposure, hereinafter the initiator also referred to as“cationic photoinitiator” or “cationic initiator”. Suitablepolyfunctional epoxy monomers include, for example,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohex-ane carboxylate,bis-(3,4-epoxycyclohexymethyl)adipate, difunctional bisphenol Aepichlorohydrin epoxy resin and multifunctionalepichlorohydrinitetraphenylol ethane epoxy resin. Suitable cationicphotoinitiators include, for example, triarylsulfoniumhexafluoroantimonate, triarylsulfonium hexafluorophosphate,diaryliodonium hexafluoroantimonate, and haloalkyl substituteds-triazine. It is noted that most cationic initiators are also freeradical initiators because, in addition to generating Bronsted acid,they also generate free radicals during photo or thermal decomposition.

In another preferred embodiment, the polymerizable monomer or oligomermay be an ethylenically unsaturated compound, having at least oneterminal ethylenic group, hereinafter also referred to as “free-radicalpolymerizable monomer”, and the initiator may be a compound, capable ofgenerating free radical, optionally in the presence of a sensitizer,upon exposure, hereinafter the initiator also referred to as “freeradical initiator”. Suitable free-radical polymerizable monomersinclude, for example, multifunctional (meth)acrylate monomers (such as(meth)acrylate esters of ethylene glycol, trimethylolpropane,pentaerythritol, ethoxylated ethylene glycol and ethoxylatedtrimethylolpropane, multifunctional urethanated (meth)acrylate, andepoxylated (meth)acrylate), and oligomeric amine diacrylates. The(meth)acrylic monomers may also have other double bond or epoxide group,in addition to (meth)acrylate group. The (meth)acrylate monomers mayalso contain an acidic (such as carboxylic acid) or basic (such asamine) functionality. Any free radical initiator capable of generatingfree radical in the presence of a sensitizer upon exposure can be usedas a free radical initiator of this invention. Suitable free-radicalinitiators include, for example, the derivatives of acetophenone (suchas 2,2-dimethoxy-2-phenylacetophenone, and2-methyl-1-[4-(methylthio)phenyl-2-morpholino propan-1-one);benzophenone; benzil; ketocoumarin (such as 3-benzoyl-7-methoxy coumarinand 7-methoxy coumarin); xanthone; thioxanthone; benzoin or analkyl-substituted anthraquinone; onium salts (such as diaryliodoniumhexafluoroantimonate, diaryliodonium triflate,(4-(2-hydroxytetradecyl-oxy)-phenyl)phenyliodonium hexafluoroantimonate,triarylsulfonium hexafluorophosphate, triarylsulfoniump-toluenesulfonate, (3-phenylpropan-2-onyl)triaryl phosphoniumhexafluoroantimonate, and N-ethoxy(2-methyl)pyridiniumhexafluorophosphate, and onium salts as described in U.S. Pat. No.5,955,238; U.S. Pat. No. 6,037,098; and U.S. Pat. No. 5,629,354); boratesalts (such as tetrabutylammonium triphenyl(n-butyl)borate,tetraethylammonium triphenyl(n-butyl)borate, diphenyliodoniumtetraphenylborate, and triphenylsulfonium triphenyl(n-butyl)borate, andborate salts as described in U.S. Pat. No. 6,232,038 and U.S. Pat. No.6,218,076); haloalkyl substituted s-triazines (such as2,4-bis(trichloromethyl)-6-(p-methoxy-styryl)-s-triazine,2,4-bis(trichloromethyl)-6-(4-methoxy-naphth-1-yl)-s-triazine,2,4-bis(trichloromethyl)-6-piperonyl-s-triazine, and2,4-bis(trichloromethyl)-6-[(4-ethoxy-ethylenoxy)-phen-1-yl]-s-triazine,and s-triazines as described in U.S. Pat. No. 5,955,238; U.S. Pat. No.6,037,098; U.S. Pat. No. 6,010,824; and U.S. Pat. No. 5,629,354); andtitanocene(bis(etha.9-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl)titanium).Onium salts, borate salts, and s-triazines are preferred free radicalinitiators. Diaryliodonium salts and triarylsulfonium salts arepreferred onium salts. Triarylalkylborate salts are preferred boratesalts. Trichloromethyl substituted s-triazines are preferreds-triazines.

In still another preferred embodiment, the polymerizable monomer oroligomer may be a combination of a monomer or oligomer including atleast one epoxy or vinyl ether functional group and a polymerizableethylenically unsaturated compound, having at least one terminalethylenic group, and the initiator may be a combination of a cationicinitiator and a free-radical initiator. A monomer or oligomer includingat least one epoxy or vinyl ether functional group and a polymerizableethylenically unsaturated compound, having at least one terminalethylenic group, can be the same compound wherein the compound containsboth ethylenic group and epoxy or vinyl ether group. Examples of suchcompounds include epoxy functional acrylic monomers, such as glycidylacrylate. The free radical initiator and the cationic initiator can bethe same compound if the compound is capable of generating both freeradical and free acid. Examples of such compounds include various oniumsalts such as diaryliodonium hexafluoroantimonate and s-triazines suchas2,4-bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen-1-yl]-s-triazinewhich are capable of generating both free radical and free acid in thepresence of a sensitizer.

The photopolymerizable coating may also include a multifunctionalmonomer. This monomer contains at least two functional groups selectedfrom an ethylenically unsaturated group and/or an epoxy or vinyl ethergroup. Particular multifunctional monomers for use in the photopolymercoating are disclosed in U.S. Pat. No. 6,410,205; U.S. Pat. No.5,049,479; EP 1079276; EP 1369232; EP 1369231; EP 1341040; U.S.2003/0124460; EP 1241002; EP 1288720; and in the reference bookincluding the cited references: Chemistry & Technology UV & EBFormulation for Coatings, Inks & Paints, Volume 2 and Prepolymers andReactive Diluents for UV and EB Curable Formulations by N. S. Allen, M.A. Johnson, P. K. T. Oldring, M. S. Salim; Edited by P. K. T. Oldring,1991, ISBN 0 947798102.

The photopolymerizable coating may also include a co-initiator.Typically, a co-initiator is used in combination with a free radicalinitiator and/or cationic initiator. Particular co-initiators for use inthe photopolymer coating are disclosed in U.S. Pat. No. 6,410,205; U.S.Pat. No. 5,049,479; EP 1079276; EP 1369232; EP 1369231; EP 1341040; U.S.2003/0124460; EP 1241002; EP 1288720; and in the reference bookincluding the cited refences: Chemistry & Technology UV & EB Formulationfor Coatings, Inks & Paints, Volume 3 and Photoinitiators for FreeRadical and Cationic Polymerisation by K. K. Dietliker, Edited by P. K.T. Oldring, 1991, ISBN 0 947798161.

The photopolymerizable coating may also include an inhibitor. Particularinhibitors for use in the photopolymer coating are disclosed in U.S.Pat. No. 6,410,205 and EP 1288720.

The photopolymerizable coating may also include a binder. The binder canbe selected from a wide series of organic polymers. Compositions ofdifferent binders can also be used. Useful binders include for examplechlorinated polyalkylene (in particular chlorinated polyethylene andchlorinated polypropylene), polymethacrylic acid alkyl esters or alkenylesters (in particular polymethyl(meth)acrylate, polyethyl(meth)acrylate,polybutyl(meth)acrylate, polyisobutyl(meth)acrylate,polyhexyl(meth)acrylate, poly(2-ethylhexyl)(meth)acrylate andpolyalkyl(meth)acrylate copolymers of (meth)acrylic acid alkyl esters oralkenyl esters with other copolymerizable monomers (in particular with(met)acrylonitrile, vinyl chloride, vinylidene chloride, styrene and/orbutadiene), polyvinyl chloride (PVC, vinylchloride/(meth)acrylonitrilecopolymers, polyvinylidene chloride (PVDC), vinylidenechloride/(meth)acrylonitrile copolymers, polyvinyl acetate, polyvinylalcohol, poly(meth)acrylonitrile, (meth)acrylonitrile/styrenecopolymers, (meth)acrylamide/alkyl (meth)acrylate copolymers,(meth)acrylonitrile/butadiene/styrene (ABS) terpolymers, polystyrene,poly(α-methylstyrene), polyamides, polyurethanes, polyesters, methylcellulose, ethylcellulose, acetyl cellulose,hydroxy-(C₁-C₄-alkyl)cellulose, carboxymethyl cellulose, polyvinylformal, and polyvinyl butyral. Other useful binders are binderscontaining carboxyl groups, in particular copolymers containingmonomeric units of α,β-unsaturated carboxylic acids or monomeric unitsof α,β-unsaturated dicarboxylic acids (preferably acrylic acid,methacrylic acid, crotonic acid, vinylacetic acid, maleic acid, oritaconic acid). By the term “copolymers” are to be understood in thecontext of the present invention as polymers containing units of atleast 2 different monomers, thus also terpolymers and higher mixedpolymers. Particular examples of useful copolymers are those containingunits of (meth)acrylic acid and units of alkyl(meth)acrylates,allyl(meth)acrylates and/or (meth)acrylonitrile as well as copolymerscontaining units of crotonic acid and units of alkyl(meth)acrylatesand/or (meth)acrylonitrile and vinylacetic acid/alkyl(meth)acrylatecopolymers. Also suitable are copolymers containing units of maleicanhydride or maleic acid monoalkyl esters. Among these are, for example,copolymers containing units of maleic anhydride and styrene, unsaturatedethers or esters or unsaturated aliphatic hydrocarbons and theesterification products obtained from such copolymers. Further suitablebinders are products obtainable from the conversion ofhydroxyl-containing polymers with intramolecular dicarboxylicanhydrides. Further useful binders are polymers in which groups withacid hydrogen atoms are present, some or all of which are converted withactivated isocyanates. Examples of these polymers are products obtainedby conversion of hydroxyl-containing polymers with aliphatic or aromaticsulfonyl isocyanates or phosphinic acid isocyanates. Also suitable arepolymers with aliphatic or aromatic hydroxyl groups, for examplecopolymers containing units of hydroxyalkyl(meth)acrylates, allylalcohol, hydroxystyrene or vinyl alcohol, as well as epoxy resins,provided they carry a sufficient number of free OH groups. Particularuseful binder and particular useful reactive binders are disclosed in EP1 369 232; EP 1 369 231; EP 1 341 040; U.S. 2003/0124460; EP 1 241 002;EP 1 288 720; U.S. Pat. No. 6,027,857; U.S. Pat. No. 6,171,735; and U.S.Pat. No. 6,420,089.

The organic polymers used as binders have a typical mean molecularweight M_(w) between 600 and 200,000, preferably between 1,000 and100,000. Preference is further given to polymers having an acid numberbetween 10 to 250, preferably 20 to 200, or a hydroxyl number between 50and 750, preferably between 100 and 500. The amount of binder(s)generally ranges from 10% to 90% by weight, preferably 20% to 80% byweight, relative to the total weight of the non-volatile components ofthe composition.

Various surfactants may be added into the photopolymerizable coating toallow or enhance the developability of the precursor. Both polymeric andsmall molecule surfactants can be used. Nonionic surfactants arepreferred. Preferred nonionic surfactants are polymers and oligomerscontaining one or more polyether (such as polyethylene glycol,polypropylene glycol, and copolymer of ethylene glycol and propyleneglycol) segments. Examples of preferred nonionic surfactants are blockcopolymers of propylene glycol and ethylene glycol (also called blockcopolymer of propylene oxide and ethylene oxide); ethoxylated orpropoxylated acrylate oligomers; and polyethoxylated alkylphenols andpolyethoxylated fatty alcohols. The nonionic surfactant is preferablyadded in an amount ranging between 0.1% and 30% by weight of thephoto-polymerizable coating, more preferably between 0.5% and 20%, andmost preferably between 1% and 15%.

A topcoat or overcoat, including, e.g., polyvinylalcohol orpolyvinylpyrrolidone or copolymers thereof may be coated on top of thephotopolymerizable coating. The contrast, obtained after exposure to IRradiation or heat, and due to the IR dye according to preferredembodiments of the present invention being present, may be obtained withor without the topcoat or overcoat.

In another preferred embodiment, the heat-sensitive coating may alsoinclude a switchable polymer which is capable of changing thehydrophilic/hydrophobic-balance of the surface of the heat-sensitivecoating upon IR-radiation or heating from hydrophilic to hydrophobic orfrom hydrophobic to hydrophilic.

The thermally switchable polymer renders the surface of theheat-sensitive coating, which is initially hydrophilic (or hydrophobic),more hydrophobic (or more hydrophilic) due to the heat generated duringthe exposure step. By more hydrophilic is meant an increase in thewettability of the coating by the fountain solution which is usually anaqueous solution. By more hydrophobic is meant an increase in thewettability of the coating by the oleophilic ink. Usually such printingplates can be used directly on the printing press, but an additional wetdeveloping step such as an on-press developing step or an off-pressdeveloping step, may be used.

Typical examples of such systems are the thermally induced acidcatalyzed cleavage of acid-labile groups pendant from a polymer backboneas described in WO 92/9934 and EP 652 483, polymeric systems whichablate from the support or which depolymerise upon heating, the thermalcyclodehydration of polyamic acids with hydrazide groups as described inU.S. Pat. No. 4,081,572, the thermally induced destruction or generationof a charge on polymers as described in EP 200 488, the thermallyinduced rupture of microcapsels and the subsequent reaction theencapsulated material with other compounds of the coating as describedin U.S. Pat. No. 5,569,573, EP 646 476, WO 94/2395, and WO 98/29258, theimage-wise crosslinking of a water-soluble bottom layer with a phenolictop layer as described in JP 10-069089, the heat-sensitive hyperbranchedpolymers containing heat-sensitive active end groups as described inU.S. Pat. No. 6,162,578, and the polarity switchable image-formingmaterials as described in EP 1 129 861.

In another preferred embodiment, the heat-sensitive coating may alsoinclude a polymer or binder soluble in an alkaline solution and asolubility inhibiting compound which reduces the solubility of the layerin the alkaline solution, and wherein, upon IR-radiation or heating, theheat-sensitive coating has an increased solubility in the alkalinesolution.

The amount of the alkali-soluble polymer is advantageously from 40% to99.8% by weight, preferably from 70% to 99.4% by weight, particularlypreferably from 80% to 99% by weight, based in each case on the totalweight of the non-volatile components of the coating. The alkali-solublebinder is preferably an organic polymer which has acidic groups with apKa of less than 13 to ensure that the coating is soluble or at leastswellable in aqueous alkaline developers. Advantageously, the binder isa polymer or polycondensate, for example a polyester, polyamide,polyurethane or polyurea. Polycondensates and polymers having freephenolic hydroxyl groups, as obtained, for example, by reacting phenol,resorcinol, a cresol, a xylenol or a trimethylphenol with aldehydes,especially formaldehyde, or ketones are also particularly suitable.Condensates of sulfamoyl- or carbamoyl-substituted aromatics andaldehydes or ketones are also suitable. Polymers ofbismethylol-substituted ureas, vinyl ethers, vinyl alcohols, vinylacetals or vinylamides and polymers of phenylacrylates and copolymers ofhydroxy-lphenylmaleimides are likewise suitable. Furthermore, polymershaving units of vinylaromatics, N-aryl(meth)acrylamides oraryl(meth)acrylates may be mentioned, it being possible for each ofthese units also to have one or more carboxyl groups, phenolic hydroxylgroups, sulfamoyl groups or carbamoyl groups. Specific examples includepolymers having units of 2-hydroxyphenyl(meth)acrylate, ofN-(4-hydroxyphenyl)(meth)acrylamide, ofN-(4-sulfamoylphenyl)-(meth)acrylamide, ofN-(4-hydroxy-3,5-dimethylbenzyl)-(meth)acrylamide, or 4-hydroxystyreneor of hydroxyphenylmaleimide. The polymers may additionally containunits of other monomers which have no acidic units. Such units includevinylaromatics, methyl(meth)acrylate, phenyl(meth)acrylate,benzyl(meth)acrylate, methacrylamide or acrylonitrile.

In a preferred embodiment, the polycondensate is a phenolic resin, suchas a novolac, a resole, or a polyvinylphenol. The novolac is preferablya cresol/formaldehyde or a cresol/xylenol/formaldehyde novolac, theamount of novolac advantageously being at least 50% by weight,preferably at least 80% by weight, based in each case on the totalweight of all binders.

In a preferred embodiment, the alkali-soluble binder is a phenolic resinwherein the phenyl group or the hydroxy group of the phenolic monomericunit are chemically modified with an organic substituent. The phenolicresins which are chemically modified with an organic substituent mayexhibit an increased chemical resistance against printing chemicals suchas fountain solutions or press chemicals such as plate cleaners.Examples of preferred chemically modified phenolic resins are describedin EP-A 0 934 822; EP-A 1 072 432; U.S. Pat. No. 5,641,608; EP-A 0 982123; WO99/01795; WO 2004/035310; WO 2004/035686; WO 2004/035645; WO2004/035687; and U.S. 2005/0037280.

A specific example of a chemically modified phenolic resin includes amonomeric unit wherein the phenyl group is substituted with a grouphaving the structure —N═N-Q, wherein the —N═N— group is covalently boundto a carbon atom of the phenyl group and wherein Q is an aromatic group.Most preferred are the polymers wherein Q has the following Formula

wherein n is 0, 1, 2, or 3;

-   wherein each R¹ is selected from hydrogen, an optionally substituted    alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl,    aralkyl or heteroaralkyl group, —SO₂—NH—R², —NH—SO₂—R⁴, —CO—NR²—R³,    —NR²—CO—R⁴, —O—CO—R⁴, —CO—O—R², —CO—R², —SO₃—R², —SO₂—R², —SO—R⁴,    —P(═O)(—O—R²) (—O—R³), —NR²—R³, —O—R², —S—R², —CN, —NO₂, a halogen,    —N-phthalimidyl, -M-N-phthalimidyl, or -M-R², wherein M represents a    divalent linking group containing 1 to 8 carbon atoms;-   wherein R², R³, R⁵ and R⁶ are independently selected from hydrogen    or an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,    heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group;-   wherein R⁴ is selected from an optionally substituted alkyl,    alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl,    aralkyl or heteroaralkyl group;-   or wherein at least two groups selected from each R¹ to R⁴ together    represent the necessary atoms to form a cyclic structure;-   or wherein R⁵ and R⁶ together represent the necessary atoms to form    a cyclic structure.

The dissolution behavior of the coating in the developer can befine-tuned by optional solubility regulating components. Moreparticularly, development accelerators and development inhibitors can beused.

Development accelerators are compounds which act as dissolutionpromoters because they are capable of increasing the dissolution rate ofthe coating. For example, cyclic acid anhydrides, phenols or organicacids can be used in order to improve the aqueous developability.Examples of the cyclic acid anhydride include phthalic anhydride,tetrahydrophthalic anhydride, hexahydrophthalic anhydride,3,6-endoxy-4-tetrahydrophthalic anhydride, tetrachlorophthalicanhydride, maleic anhydride, chloromaleic anhydride, alpha-phenylmaleicanhydride, succinic anhydride, and pyromellitic anhydride, as describedin U.S. Pat. No. 4,115,128. Examples of the phenols include bisphenol A,p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone,2,3,4-trihydroxy-benzophenone, 4-hydroxybenzophenone,4,4′,4″-trihydroxy-triphenylmethane, and4,4′,3″,4″-tetrahydroxy-3,5,3′,5′-tetramethyltriphenyl-methane, and thelike. Examples of the organic acids include sulfonic acids, sulfinicacids, alkylsulfuric acids, phosphonic acids, phosphates, and carboxylicacids, as described in, for example, JP-A 60-88,942 and JP-A 2-96,755.Specific examples of these organic acids include p-toluenesulfonic acid,dodecylbenzenesulfonic acid, p-toluenesulfinic acid, ethylsulfuric acid,phenylphosphonic acid, phenylphosphinic acid, phenyl phosphate, diphenylphosphate, benzoic acid, isophthalic acid, adipic acid, p-toluic acid,3,4-dimethoxybenzoic acid, 3,4,5-trimethoxybenzoic acid,3,4,5-trimethoxycinnamic acid, phthalic acid, terephthalic acid,4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid,n-undecanoic acid, and ascorbic acid. The amount of the cyclic acidanhydride, phenol, or organic acid contained in the coating ispreferably in the range of 0.05% to 20% by weight.

In a preferred embodiment, the coating also contains one or moredissolution inhibitors, i.e., one or more materials which reduce thedissolution rate of the hydrophobic polymer in the aqueous alkalinedeveloper at the non-exposed areas of the coating. The dissolutioninhibiting capability of the inhibitor can easily be tested by coatingtwo samples on a support: a reference sample containing only thehydrophobic polymer and another including both the polymer (in equalamounts as the reference) as well as the inhibitor. A series ofunexposed samples is immersed in an aqueous alkaline developer, eachsample during a different time period. After the immersion period, thesample is removed from the developer, immediately rinsed with water,dried and then the dissolution of the coating in the developer ismeasured by comparing the weight of the sample before and after thedevelopment. As soon as the coating is dissolved completely, no moreweight loss is measured upon longer immersion time periods, i.e., acurve representing weight loss as a function of immersion time reaches aplateau from the moment of complete dissolution of the layer. A materialhas good inhibiting capability when the coating of the sample withoutthe inhibitor has dissolved completely in the developer before thesample with the inhibitor is attacked by the developer to such an extentthat the ink-accepting capability of the coating is affected.

The dissolution inhibitor(s) can be added to the layer of the coatingwhich includes the alkali-soluble hydrophobic polymer discussed above.In this preferred embodiment, the dissolution rate of the non-exposedcoating in the developer is reduced by interaction between thehydrophobic polymer and the inhibitor, due to, e.g., hydrogen bondingbetween these compounds. The dissolution inhibiting capability of theinhibitor is preferably reduced or destroyed by the heat generatedduring the exposure so that the coating readily dissolves in thedeveloper at exposed areas. Such inhibitors are preferably organiccompounds which include at least one aromatic group and a hydrogenbonding site, e.g., a carbonyl group, a sulfonyl group, or a nitrogenatom which may be quaternized and which may be part of a heterocyclicring or which may be part of an amino substituent of the organiccompound. Suitable dissolution inhibitors of this type have beendisclosed in e.g., EP-A 825927, WO 97/39894, and EP-A 823327. Some ofthe compounds mentioned below, e.g., infrared dyes such as cyanines andcontrast dyes such as quaternized triarylmethane dyes can also act as adissolution inhibitor.

Water-repellent polymers represent a second type of suitable dissolutioninhibitors. Such polymers seem to increase the developer resistance ofthe coating by repelling the aqueous developer from the coating. Thewater-repellent polymers can be added to the layer including thehydrophobic polymer and/or can be present in a separate layer providedon top of the layer with the hydrophobic polymer. In the latterpreferred embodiment, the water-repellent polymer forms a barrier layerwhich shields the coating from the developer and the solubility of thebarrier layer in the developer or the penetrability of the barrier layerby the developer can be reduced by exposure to heat or infrared light,as described in, e.g., EP-A 864420, EP-A 950517, and WO99/21725.Preferred examples of the water-repellent polymers are polymersincluding siloxane and/or perfluoroalkyl units. In one preferredembodiment, the coating contains such a water-repellent polymer in anamount between 0.5 mg/m² and 25 mg/m², preferably between 0.5 mg/m² and15 mg/m² and most preferably between 0.5 mg/m² and 10 mg/m². When thewater-repellent polymer is also ink-repelling, e.g., in the case ofpolysiloxanes, higher amounts than 25 mg/m² can result in poorink-acceptance of the non-exposed areas. An amount lower than 0.5 mg/m²on the other hand may lead to an unsatisfactory development resistance.The polysiloxane may be a linear, cyclic or complex cross-linked polymeror copolymer. The term polysiloxane compound shall include any compoundwhich contains more than one siloxane group —Si(R,R′)—O—, wherein R andR′ are optionally substituted alkyl or aryl groups. Preferred siloxanesare phenylalkylsiloxanes and dialkylsiloxanes. The number of siloxanegroups in the (co)polymer is at least 2, preferably at least 10, morepreferably at least 20. It may be less than 100, preferably less than60. In another preferred embodiment, the water-repellent polymer is ablock-copolymer or a graft-copolymer of a poly(alkylene oxide) block anda block of a polymer including siloxane and/or perfluoroalkyl units. Asuitable copolymer includes about 15 to 25 siloxane units and 50 to 70alkylene oxide groups. Preferred examples include copolymers includingphenylmethylsiloxane and/or dimethylsiloxane as well as ethylene oxideand/or propylene oxide, such as Tego Glide 410, Tego Wet 265, TegoProtect 5001 or Silikophen P50/X, all commercially available from TegoChemie, Essen, Germany. Such a copolymer acts as a surfactant which uponcoating, due to its bifunctional structure, automatically positionsitself at the interface between the coating and air and thereby forms aseparate top layer even when the whole coating is applied from a singlecoating solution. Simultaneously, such surfactants act as a spreadingagent which improves the coating quality. Alternatively, thewater-repellent polymer can be applied in a second solution, coated ontop of the layer including the hydrophobic polymer. In that preferredembodiment, it may be advantageous to use a solvent in the secondcoating solution that is not capable of dissolving the ingredientspresent in the first layer so that a highly concentrated water-repellentphase is obtained at the top of the coating.

The heat-sensitive coating may also include a composition which istypically used for a driographic printing plate, usually based oncopolymers of polysiloxane.

Examples Synthesis of IRD-001 (scheme 1)

SM-001 is prepared as described in U.S. Pat. No. 5,576,443; SM-001 (8.14g) is dissolved in methanol (30 ml); SM-002 (2.12 g) and triethylamine(1.66 ml) are added. After stirring for 1 hour at room temperature, thereaction mixture is diluted with ethyl acetate (150 ml) andmethanesulfonic acid (0.77 ml) is added, inducing the crystallization ofIRD-001. Upon filtration, washing with ethyl acetate and drying undervacuum, IRD-001 is obtained as a red-brown crystalline powder (5.2 g).Absorption maximum (methanol): 818 nm.

Synthesis of IRD-002 (scheme 2):

SM-001 is prepared as described in U.S. Pat. No. 5,576,443; SM-001 (4.90g) is dissolved in methanol (20 ml); SM-003 (2.00 g) and triethylamine(1.86 ml) are added. After stirring for 1 hour at room temperature,NaOAc-3H₂O (1.64 g)(NaOAc means sodium acetate) and acetone (400 ml) areadded, inducing the crystallization of IRD-002. Upon filtration, washingwith acetone and drying under vacuum, IRD-002 is obtained as a greencrystalline powder (4.81 g). Absorption maximum (methanol): 812 nm.

Synthesis of IRD-003 (scheme 3)

SM-001 is prepared as described in U.S. Pat. No. 5,576,443. To asolution of SM-001 (203.8 g) in methanol (800 ml) at room temperature isadded a 1.5 molar solution of NH₄OH in water (1.0 l). After stirring for4 hours at 50° C., isopropanol (200 ml) is added and the reactionmixture is cooled overnight. The precipitate is filtered, washed withcold isopropanol and air dried to obtain INT-001 (160.0 g) as a goldcolored powder.

INT-001 (160.0 g) is dissolved in methanol (1.5 1) and under strongstirring, a solution of KOH (31.5 g) in water (62 ml) is added in 30minutes. After stirring for 90 minutes at room temperature, theprecipitate is filtered, washed with ethanol (2×100 ml) on the filterand air dried to obtain INT-002 (160.2 g).

To a solution of INT-002 (0.732 g) in DMSO at room temperature is addedSM-004 (0.65 g) and the potassium salt of tertiary butanol (hereafter:Kot-Bu) (0.25 g). After stirring at room temperature for 1 hour,additional SM-004 (0.22 g) and Kot-Bu (0.13 g) are added and thereaction mixture is stirred at 40° C. for 2 hours. After cooling andneutralization with acetic acid, the reaction mixture is poured intomethyl t.butyl ether (MTBE) (150 ml). After settling, the solution isdecanted. The precipitate is treated with MTBE (100 ml), filtered toobtain IRD-003 (0.82 g). Absorption maximum (methanol): 788 nm.

Synthesis of IRD-004 (scheme 4)

SM-001 is prepared as described in U.S. Pat. No. 5,576,443. To asolution of SM-001 (203.6 g) in methanol (600 ml) at room temperature isadded a 40% w/w solution of methyl amine in water (200 ml). Afterstirring for 1 hour at 40° C., isopropanol (250 ml) is added and thereaction mixture is cooled to 5° C. The precipitate is filtered, washedwith an ice cold 9/1 mixture of isopropanol and water (2×100 ml) and airdried, to obtain INT-003 (181.5 g). INT-003 (181.1 g) is dissolved inmethanol (1.8 l) and under strong stirring, a solution of KOH (41.6 g)in water (120 ml) is added in 30 minutes. After stirring for 1 hour atroom temperature, the reaction mixture is cooled to 15° C. and theprecipitate is filtered, washed with cold ethanol (2×100 ml) on thefilter and air dried to obtain INT-004 (160.9 g). To a suspension ofINT-004 (7.46 g) in DMSO (30 ml) are added SM-004 (8.73 g) and KOt.Bu(1.35 g). After stirring for 3 days at room temperature, cooling to 5°C. addition of methanesulfonic acid (0.78 ml), IRD-004 is precipitatedwith a mixture of ethylacetate/water (100/1) (200 ml). After suspendingin acetone, filtration and drying, IRD-004 (8.61 g) is obtained.Absorption maximum (methanol): 812 nm.

Synthesis of IRD-005 (scheme 5

SM-001 is prepared as described in U.S. Pat. No. 5,576,443. To asuspension of SM-001 (8.14 g) and SM-005 (3.03 g) in sulfolane (60 ml)at room temperature is added Kot-Bu (3.36 g). After stirring for 30minutes at 90° C., the reaction mixture is cooled to room temperatureand upon addition of methanesulfonic acid (1.3 ml), water (3 ml) andacetone (120 ml), crude IRD-005 precipitates. After filtration,dissolving in water (20 ml) and addition of acetone (500 ml), IRD-005(9.24 g, containing CH₃SO₃K as an impurity) is obtained. Absorptionmaximum (methanol+HOAc): 806 nm. Absorption maximum (methanol+Et₃N): 654nm.

Synthesis of IRD-006 (scheme 6)

SM-001 is prepared as described in U.S. Pat. No. 5,576,443. To a stirredsolution of SM-001 (81.5 g) in methanol (250 ml) at room temperature isadded a solution of KOAc (11.8 g) in methanol (200 ml). Upon addition ofmethanol (200 ml) and ethyl acetate (300 ml), crude INT-005 is obtainedby filtration. After washing with ethyl acetate (200 ml) and dryingunder vacuum INT-005 (55 g) is obtained, ready for use in the next step.After warming a suspension of INT-005 (5.00 g) and SM-006 (3.4 g) insulfolane (30 ml) to 60° C., KOt.Bu (3.36 g) is added. After stirringfor 30 minutes at 90° C., the reaction mixture is cooled to roomtemperature and upon addition of water (10 ml), methanesulfonic acid(0.65 ml) and acetone (500 ml), IRD-006 precipitates. After filtrationIRD-006 (6.74 g, containing CH₃SO₃K as an impurity) is obtained.Absorption maximum (methanol): 820 nm.

Synthesis of IRD-007, IRD-008, and IRD-009

The synthesis of IRD-007, IRD-008, and IRD-009 is performed in analogywith the synthesis of IRD-006, replacing with SM-007, SM-008, and SM-009(scheme 7), respectively.

-   Absorption maximum (methanol) of IRD-007: 830 nm.-   Absorption maximum (methanol) of IRD-008: 826 nm.-   Absorption maximum (methanol) of IRD-009: 829 nm.

Synthesis of IRD-057: scheme 8

SM-010 is prepared as described in Tetrahedron, 50 (1994) 5579-90.SM-001 is prepared as described in U.S. Pat. No. 5,576,443. To asuspension of SM-001 (34.2 g) and SM-010 (15 g) in acetonitrile (100 ml)12.7 ml triethyl amine is added; the mixture is heated for 2 hours at80° C. After cooling to room temperature, ethyl acetate (400 ml),containing water (8 ml) is added. After stirring for 1 hour, the crudeIRD-057 is filtered off. Crude IRD-057 is purified by dissolution inacetonitrile (50 ml) and precipitation with acetone (1000 ml); afterfiltration and drying under vacuum, 23.6 g IRD-057 is obtained as agreen powder.

Synthesis of IRD-068 and IRD-069: scheme 9

The synthesis of SM-011 is described in EP 0 626 427; SM-012 iscommercially available from TCI organic chemicals; SM-013, methyltriflate, is commercially available from Aldrich; SM-014, sodiumtetraphenyl borate, is commercially available from Aldrich. To asuspension of 30 g SM-011 and 18 g SM-012 in 50 ml sulfolane at roomtemperature, 13.3 ml triethyl amine was added; this mixture was heatedat 90° C. for 2 hours. After cooling the mixture to room temperature,200 ml methanol is added to precipitate INT-006. After filtration,washing with 100 ml methanol and drying, 22 g INT-006, only slightlycontaminated with SM-001, was obtained. To a solution of 21 g INT-006 in50 ml methylene chloride 7.1 g of SM-013 (methyl trifluoromethanesulfonate=methyl triflate) was added at room temperature. After 2 hours,2 g of triethyl amine was added, followed by 200 ml ethyl acetate toprecipitate IRD-068. After filtration, crude IRD-068 was purified bydissolution in 50 ml methylene chloride, addition of 2 g triethyl amine,followed by 200 ml ethyl acetate. After filtration and drying undervacuum, 20 g IRD-068 was obtained. To a solution of 10 g IRD-068 in 300ml methanol at 60° C., a solution of 4.58 g SM-014 in 100 ml methanolwas added. After cooling to room temperature during 1 hour, theprecipitated IRD-069 was filtered and purified as follows: washing with200 ml water/filtration; washing with 200 ml methanol/filtration/dryingunder vacuum. 11.4 IRD-069 was obtained.

Synthesis of IRD-072: scheme 10

To a solution of 4.5 g SM-017 (commercially available from SpectrumInfo) in 155 ml toluene at 110° C. 3.0 g of SM-018 (synthesis accordingto Organic Letters 2001, 3(14), 2241-2243) was added. After 4 hours at110° C., the reaction mixture was cooled to room temperature, allowingIRD-072 to crystallize. After washing the powder 3 times with 50 ml hottoluene and drying in vacuum, 6.3 g of IRD-072 was obtained as a greenpowder.

Synthesis of IRD-083: scheme 11

To a solution of 425 mg SM-019 (commercially available from SpectrumInfo) in 15.5 ml toluene at 110° C., 301 mg of SM-018 (synthesizedaccording to Organic Letters 2001, 3(14), 2241-2243) was added. Afterheating for 2 hours at 110° C., the reaction mixture was cooled to 50°C., allowing IRD-083 to crystallize. After washing the powder with 5 mlof hot toluene and drying in vacuum, 250 mg of IRD-083 is obtained as agreen powder.

Synthesis of IRD-096: scheme 12

A suspension of 50 g SM-011 (synthesis described in EP 0 626 427) and31.7 g SM-015 (commercially is commercially available from Aldrich) inmethanol was warmed to 70° C. followed by the addition of a 33% solutionof sodium methoxide in 29 g of methanol. After 4 hours, the reactionmixture was cooled to room temperature. The precipitated INT-007 wasfiltered and purified as follows: washing with 100 ml ethylacetate/filtration/washing with 100 ml water/filtration/drying undervacuum. 35.1 INT-007 was obtained. To a suspension of 1.2 g INT-007 in 5ml acetonitrile 264 mg SM-016 was added SM-016. After heating thereaction mixture for 1 hour at 70° C., 332 mg of potassium iodide wasadded. After 6 hours at 70° C., the reaction mixture was cooled to roomtemperature and filtered. Upon addition of 20 ml ethyl acetate to themother liquor, IRD-071 was precipitated. After filtration and dryingunder vacuum 670 mg of IRD-096 was obtained.

Preparation of the Lithographic Substrate S-01

A 0.19 mm thick aluminum foil was degreased by immersing the foil in anaqueous solution containing 40 g/l of sodium hydroxide at 60° C. for 8seconds and rinsed with demineralized water for 2 seconds. The foil wasthen electrochemically grained during 15 seconds using an alternatingcurrent in an aqueous solution containing 12 g/l of hydrochloric acidand 38 g/l of aluminum sulfate (18-hydrate) at a temperature of 33° C.and a current density of 130 A/dm². After rinsing with demineralizedwater for 2 seconds, the aluminum foil was then desmutted by etchingwith an aqueous solution containing 155 g/l of sulfuric acid at 70° C.for 4 seconds and rinsed with demineralized water at 25° C. for 2seconds. The foil was subsequently subjected to anodic oxidation during13 seconds in an aqueous solution containing 155 g/l of sulfuric acid ata temperature of 45° C. and a current density of 22 A/dm², then washedwith demineralized water for 2 seconds and post-treated for 10 secondswith a solution containing 4 g/l of polyvinylphosphonic acid at 40° C.,rinsed with demineralized water at 20° C. during 2 seconds and dried.

The support thus obtained has a surface roughness Ra of 0.21 μm and ananodic weight of 4 g/m² of Al₂O₃.

Comparative Examples 1 to 3 and Invention Examples 1 to 18 Preparationof the Printing Plate Precursors PPP-01 to PPP-21

The printing plate precursors PPP-01 to PPP-21 were produced by applyinga coating solution onto the above described lithographic substrate S-01.The composition of the coating is defined in Table 1. The pH of thecoating solution was adjusted to 3.6 before coating. The coating wasapplied from an aqueous solution. The coatings were dried at 50° C. for1 minute. The coating weights of the ingredients are indicated in Table1.

Comparative IR-DYES:

TABLE 1 Composition of Printing Plate Precursors Coating Coating CoatingCoating Coating weight weight IR- weight weight weight PPP- PSAN (1)Type dye (2) PAA (3) PVA (4) ZONYL (5) number (g/m²) IR-dye (mol/m²)(g/m²) (g/m²) (g/m²) PPP-01 0.6927 CIR-01 1.03 10⁻⁴ 0.090 — 0.0075PPP-02 0.6927 CIR-02 1.10 10⁻⁴ 0.090 — 0.0075 PPP-03 0.6927 CIR-02 1.1010⁻⁴ — 0.090 0.0075 PPP-04 0.6927 IRD-006 0.75 10⁻⁴ 0.090 — 0.0075PPP-05 0.6927 IRD-006 0.75 10⁻⁴ — 0.090 0.0075 PPP-06 0.6927 IRD-0070.83 10⁻⁴ 0.090 — 0.0075 PPP-07 0.6927 IRD-007 0.83 10⁻⁴ — 0.090 0.0075PPP-08 0.6927 IRD-009 0.85 10⁻⁴ 0.090 — 0.0075 PPP-09 0.6927 IRD-0090.85 10⁻⁴ — 0.090 0.0075 PPP-10 0.6927 IRD-004 1.10 10⁻⁴ 0.090 — 0.0075PPP-11 0.6927 IRD-004 1.10 10⁻⁴ — 0.090 0.0075 PPP-12 0.6927 IRD-0031.10 10⁻⁴ 0.090 — 0.0075 PPP-13 0.6927 IRD-003 1.10 10⁻⁴ — 0.090 0.0075PPP-14 0.6927 IRD-008 0.82 10⁻⁴ 0.090 — 0.0075 PPP-15 0.6927 IRD-0080.82 10⁻⁴ — 0.090 0.0075 PPP-16 0.6927 IRD-005 0.87 10⁻⁴ 0.090 — 0.0075PPP-17 0.6927 IRD-005 0.87 10⁻⁴ — 0.090 0.0075 PPP-18 0.6927 IRD-0011.10 10⁻⁴ 0.090 — 0.0075 PPP-19 0.6927 IRD-001 1.10 10⁻⁴ — 0.090 0.0075PPP-20 0.6927 IRD-002 1.10 10⁻⁴ 0.090 — 0.0075 PPP-21 0.6927 IRD-0021.10 10⁻⁴ — 0.090 0.0075 (1) PSAN is a latex dispersion of aStyrene/acrylonitrile copolymer (molar ratio 50/50; stabilized with ananionic wetting agent; average particle size 61 nm; solid content byweight 20.58%); (2) IR-dye is added as an aqueous solution or dispersionto the coating; (3) PAA is Glascol E15 from Allied ColloidsManufacturing Co. Ltd; a polyacrylic acid of 15% wt in water; (4) PVA isan aqueous solution of ERKOL WX48/20, a polyvinyalcohol/polyvinylacetatecopolymer (7.5% wt) from ERKOL, part of ACETEX Group; (5) ZONYL is ZonylFSO100, a surfactant from Dupont.

Image Formation

The printing plate precursors PPP-01 to PPP-11 were exposed with a CreoTrendsetter (40 W) at several exposure energy densities, namely 0, 125,200, 275, and 350 mJ/cm². The Diffuse Reflectance Spectra (DRS-spectra)were measured with a SHIMADZU UV-3101 PC/ISR-3100 spectrophotometer foreach plate precursor at areas exposed with these energies. From theseDRS-spectra, the optical density was calculated by integration over thewavelength range from 400 nm to 700 nm. The difference between theintegrated optical density on the exposed area and the integratedoptical density on the non-exposed area is equal to the contrast-valueas given in Table 2 for Comparative Examples 1 to 3 and InventionExamples 1 to 8.

For the printing plate precursors PPP-12 to PPP-21 the contrast-valueswere calculated in the same way for the exposure energies of 200 and 275mJ/cm². These values are given in Table 3 for Invention Examples 9 to18.

TABLE 2 Contrast-values of Print-out Images Contrast- Contrast-Contrast- Contrast- value value value value EXAMPLE PPP- at 125 at 200at 275 at 350 number number mJ/cm² mJ/cm² mJ/cm² mJ/cm² ComparativePPP-01 −5.45 −12.99 −23.28 −36.67 Example 1 Comparative PPP-02 −12.45−0.31 −6.42 −10.32 Example 2 Comparative PPP-03 −11.52 −9.69 −15.33−19.87 Example 3 Invention PPP-04 12.60 55.69 46.36 40.68 Example 1Invention PPP-05 7.53 37.17 40.25 34.57 Example 2 Invention PPP-06 21.3566.18 55.10 49.75 Example 3 Invention PPP-07 14.78 46.19 48.02 44.63Example 4 Invention PPP-08 3.88 40.89 30.68 24.07 Example 5 InventionPPP-09 7.29 31.48 35.58 30.10 Example 6 Invention PPP-10 16.00 46.2026.76 17.85 Example 7 Invention PPP-11 10.76 34.27 26.31 14.49 Example 8

TABLE 3 Contrast-values of Print-out Images EXAMPLE PPP- Contrast-valueContrast-value number number at 200 mJ/cm² at 275 mJ/cm² InventionPPP-12 23.29 24.40 Example 9 Invention PPP-13 2.14 4.68 Example 10Invention PPP-14 33.84 21.86 Example 11 Invention PPP-15 27.97 30.70Example 12 Invention PPP-16 38.99 46.95 Example 13 Invention PPP-17 7.994.67 Example 14 Invention PPP-18 19.25 6.66 Example 15 Invention PPP-1913.60 8.88 Example 16 Invention PPP-20 18.69 0.65 Example 17 InventionPPP-21 25.86 28.23 Example 18

A negative value indicates that the optical density on the exposed areasis lower than before the exposure due to the decomposition of the IR-dyeresulting in bleaching of the coating upon exposure.

A positive value indicates an increase of the visual optical density onthe exposed area compared with the non-exposed area. The higher thisvalue, the higher the contrast of the print-out image build-up uponexposure.

In the Comparative Examples 1 to 3, a negative value is observed for thecomparative IR-dyes CIR-01 and CIR-02. The decrease of the visualoptical density after exposure demonstrates the bleaching process inthese Comparative Examples 1 to 3 wherein no substantial optical densitywas build up upon exposure.

As an example, the absorption spectra of PPP-01, including CIR-01(comparative dye) and PPP-04, including IRD-006 (invention dye), exposedwith different energies (0, 125, 200, 275, and 350 mJ/cm²) are given inFIG. 1 and FIG. 2: the absorption above about 600 nm decreases withincreasing exposure energy, but only for the invention example theabsorption in the visual wavelength range is increased after exposure,indicating the build-up of a colored print-out image.

Comparative Example 4 and Invention Example 19 Preparation of thePrinting Plate Precursors PPP-22 and PPP-23

The printing plate precursors PPP-22 and PPP-23 were produced in thesame way as described above for PPP-01. The coating weights of theingredients are indicated in Table 4.

TABLE 4 Composition of Printing Plate Precursors Coating Coating CoatingCoating weight weight IR- weight weight PPP- PSAN (1) Type dye (2) PAA(3) ZONYL (5) number (g/m²) IR-dye (g/m²) (g/m²) (g/m²) PPP-22 0.60CIR-01 0.096 0.120 0.007 PPP-23 0.60 IRD-004 0.116 0.120 0.007 (1) to(5): see Table 1

Image Formation

The printing plate precursors PPP-22 and PPP-23 were exposed with a CreoS059 plate setter (exposure energy 100-300 mJ/cm²). In Invention Example19 (for PPP-23) a very good and pronounced print-out image is observedwhile in Comparative Example 4 (for PPP-22) it was difficult to observea difference between the exposed and non-exposed areas.

Print Results

After exposure, the plates were mounted on a GTO46 printing press(available from Heidelberger Druckmaschinen A G), and a print job wasstarted using K+E Novavit 800 Skinnex ink (trademark of BASFDrucksysteme GmbH) and 3% FS101 (trademark of AGFA) in 10% isopropanolas fountain liquid.

In the Invention Example 19 (for PPP-23) a better clean-out in thenon-exposed areas of the plate was observed than in the ComparativeExample 4 (for PPP-22). This indicates less adsorption of the IR-dye ofa preferred embodiment of the present invention on the hydrophilicsurface of the aluminum support. Good results are obtained for the otherlithographic printing properties of the plates.

Comparative Example 5 and Invention Examples 20 and 21 Preparation ofthe Printing Plate Precursors PPP-24 to PPP-26

The printing plate precursors PPP-24 to PPP-26 were produced in the sameway as described above for PPP-01. The coating weights of theingredients are indicated in Table 5.

TABLE 5 Composition of Printing Plate Precursors Coating Coating CoatingCoating weight weight IR- weight weight PPP- PSAN (1) Type dye (2) PAA(3) ZONYL (5) number (g/m²) IR-dye (g/m²) (g/m²) (g/m²) PPP-24 0.59CIR-01 0.1 0.12 0.01 PPP-25 0.59 IRD-004 0.11 0.12 0.01 PPP-26 0.59IRD-007 0.12 0.12 0.01 (1) to (5): see Table 1

Image Formation

The printing plate precursors PPP-24 to PPP-26 were exposed with a CreoTH5850 (40 W) plate setter at exposure energies varying between 150 and300 mJ/cm². The contrast-values of these print-out images have beencalculated from the DRS-spectra as described in Invention Example 1 andare given in Table 6.

TABLE 6 Contrast-values of Print-out Images Contrast- Contrast-Contrast- Contrast- value value value value EXAMPLE PPP- at 150 at 200at 250 at 300 number number mJ/cm² mJ/cm² mJ/cm² mJ/cm² ComparativePPP-24 −13.57 −21.09 −22.58 −21.77 Example 5 Invention PPP-25 14.7721.60 22.26 27.35 Example 20 Invention PPP-26 6.70 21.91 32.16 39.14Example 21The positive contrast-values for Invention Example 20 (for PPP-25) andInvention Example 21 (for PPP-26) demonstrate a very good and pronouncedprint-out image. The negative contrast-values for Comparative Example 5(for PPP-24) demonstrate the weak differentiation between the exposedand non-exposed areas.

Print Results

After exposure, the plates were mounted on a GTO46 printing press(available from Heidelberger Druckmaschinen A G), and a print job wasstarted using K+E Novavit 800 Skinnex ink (trademark of BASFDrucksysteme GmbH) and 3% FS101 (trademark of AGFA) in 10% isopropanolas fountain liquid.

In the Invention Example 20 (for PPP-25) and Invention Example 21 (forPPP-26) a better clean-out in the non-exposed areas of the plate wasobserved than in the Comparative Example 5 (for PPP-24). This indicatesless adsorption of the IR-dye according to preferred embodiments of theinvention on the hydrophilic surface of the aluminum support. Goodresults are obtained for the other lithographic printing properties ofthe plates.

Comparative Example 6 and Invention Examples 22 and 24 Preparation ofthe Printing Plate Precursors PPP-27 to PPP-30

The printing plate precursors PPP-27 to PPP-30 were produced in the sameway as described above for PPP-01. The PPP-28 contains, in addition to acomparative IR-dye, a Cu-phthalocyanine (CD-01) as contrast dye, able toform a visual contrast after processing. The coating weights of theingredients are indicated in Table 7.

TABLE 7 Composition of Printing Plate Precursors Coating Coating Coatingweight Coating Coating weight weight IR- weight weight ZONYL PPP- PSAN(1) Type dye (2) CD-01 PAA (3) (5) number (g/m²) IR-dye (g/m²) (g/m²)(g/m²) (g/m²) PPP-27 0.62 CIR-01 0.08 — 0.08 0.01 PPP-28 0.62 CIR-010.08 0.02 0.08 0.01 PPP-29 0.62 IRD-004 0.09 — 0.08 0.01 PPP-30 0.62IRD-007 0.10 — 0.08 0.01 (1) to (5): see Table 1 CD-01 is aCu-phthalocyanine contrast dye from Cabot Corporation, an aqueousdispersion of 15 wt %.

Image Formation

The printing plate precursors PPP-27 to PPP-30 were exposed with a CreoTH5850 (40 W) plate setter at exposure energies varying between 150 and300 mJ/cm². The contrast-values of these print-out images have beencalculated from the DRS-spectra as described in Invention Example 1 andare given in Table 8.

TABLE 8 Contrast-values of Print-out Images Contrast- Contrast-Contrast- Contrast- value value value value EXAMPLE PPP- at 150 at 200at 250 at 300 number number mJ/cm² mJ/cm² mJ/cm² mJ/cm² ComparativePPP-27 −9.38 −13.81 −16.99 −16.79 Example 6 Comparative PPP-28 −8.54−12.35 −14.34 −12.14 Example 7 Invention PPP-29 13.67 27.59 35.19 33.05Example 22 Invention PPP-30 12.22 30.17 37.42 36.28 Example 23

The positive contrast-values for Invention Example 22 (for PPP-29) andInvention Example 23 (for PPP-30) demonstrate a very good and pronouncedprint-out image. The negative contrast-values for Comparative Example 6(for PPP-27) demonstrate the weak differentiation between the exposedand non-exposed areas. The presence of the contrast dye CD-01(Cu-phthalocyanine) gives also no rise to an increase of thecontrast-value upon exposure as demonstrate in Comparative Example 7(for PPP-28).

Processing

After exposure, the printing plate precursors were developed in agumming unit, using with Agfa RC5230 (trademark from AGFA) as gummingsolution. The RC520 solution is an aqueous solution of the surfactantDOWFAX 3B2, commercially available from DOW CHEMICAL, in a concentrationof 39.3 g/l, citric acid.laq in a concentration of 9.8 g/l, andtrisodium citrate.2aq in a concentration of 32.6 g/l, and the RC520solution has a pH-value of about 5.

In the developing step, the non-exposed areas are removed from thesupport revealing the hydrophilic surface of the aluminum support whilethe exposed areas remain on the plate. The DRS-spectra of the exposedand non-exposed area after this wet processing were measured and fromthese spectra the absorption was integrated over the wavelength rangebetween 400 and 700 nm. The contrast-value after processing is definedas the difference between the integrated value of the exposed area andthe non-exposed area. These contrast-values, which are different fromthe contrast-values of the print-out images, are given in Table 9.

TABLE 9 Contrast-values after Processing Contrast- Contrast- Contrast-Contrast- value value value value after after after after processingprocessing processing processing EXAMPLE PPP- at 150 at 200 at 250 at300 number number mJ/cm² mJ/cm² Mj/cm² mJ/cm² Comparative PPP- 36.3333.10 32.31 30.34 Example 6 27 Comparative PPP- 66.85 65.94 63.88 60.77Example 7 28 Invention PPP- 95.03 110.57 109.23 100.83 Example 22 29Invention PPP- 62.89 80.78 83.17 81.86 Example 23 30

After processing, the coating layer is removed on the non-exposed areas,revealing the hydrophilic surface of the aluminum support, while on theexposed area the coating remains on the plate. For the ComparativeExample 6 (PPP-27) these values vary between 30 and 36 which may beconsidered as a weak contrast after processing.

In order to increase this contrast, typically a contrast dye (e.g.,CD-01) was added in the coating composition (PPP-28), resulting in goodcontrast-value ranging between 60 and 66 as demonstrated in ComparativeExample 7.

In Invention Examples 22 and 23, including the IR-dyes of the presentinvention, contrast-values ranging of about 80 or even about 100 to 110were obtained as demonstrated in Table 9. This is clearly an additionaladvantage of the IR-dyes of the present invention beside the improvedcontrast of the print-out images as demonstrated in Table 8.

Print Results

The plates were mounted on a GTO46 printing press (available fromHeidelberger Druckmaschinen A G), and a print job was started using K+ENovavit 800 Skinnex ink (trademark of BASF Drucksysteme GmbH) and 3%FS101 (trademark of AGFA) in 10% isopropanol as fountain liquid. Goodprinting results are obtained with the plates.

Comparative Example 8 and Invention Example 24 Preparation ofLithographic Substrate S-02

A 0.28 mm thick aluminum support was degreased by spraying it with anaqueous solution containing 34 g/l of sodium hydroxide at 70° C. for 5.9s and rinsing it at room temperature for 3.6 s with a solutioncontaining 12.4 g/l hydrochloric acid and 9 g/l sulphuric acid.

The aluminum support was than electrochemically grained using analternating current in an aqueous solution containing 12.4 g/lhydrochloric acid and 9 g/l sulphuric acid at a temperature of 37° C.and at an anodization charge density of 54500 Coulomb/m².

Subsequently, the support was etched with an aqueous solution containing145 g/l sulphuric acid at 80° C. for 4.8 s and rinsed with water at roomtemperature for 3.6 s.

After the etching step, the support was subjected for 4.6 s to an anodicoxidation in an aqueous solution containing 145 g/l sulphuric acid and10 g/l aluminum sulphate at a temperature of 57° C. and a currentdensity of 2500 A/m². Subsequently, the anodized support was washed withwater at room temperature for 3.6 s and dried at 55° C. for 5.3 s.

Subsequently the support was post-anodic treated with 2.2 g/lpolyvinylphosphonic acid during 4.2 s at 70° C. and rinsed with waterfor 1.2 s at room temperature.

The obtained support was processed in a TD6000 developer (trademark ofAGFA) at 25° C. during 22 s to remove the post-anodic treatment andsubsequently rinsed with water. After this, the substrate was gummedwith RC795 (trademark of AGFA).

The grained and anodized aluminum support was washed with water anddried at 40° C. during 15 minutes.

Preparation of the Printing Plate Precursors PPP-31 and PPP-32

The printing plate precursors PPP-31 and PPP-32 were produced by coatinga solution of 0.67 g IR-dye in 100 ml ethanol with a doctor blade at awet thickness of 30 μm onto the above described lithographic substrateS-02. After drying the coating weights of the ingredients are indicatedin Table 10.

TABLE 10 Composition of Printing Plate Precursors Type Coating weightPPP-number IR-dye IR-dye (2) (g/m²) PPP-31 CIR-03 0.67 PPP-32 IRD-0040.67

Image Formation

The printing plate precursors PPP-31 and PPP-32 were exposed with anIR-laser diode at 830 nm. The energy densities vary between 357 and 1000mJ/cm² as indicated in Table 11 (different settings for Laser Power andDrum Speed).

TABLE 11 Applied Laser Energy Densities Laser Power Drum Speed PitchLaser Energy (mW) (m/s) (μm) Density (mJ/cm²) 200 8 7 357 280 8 7 500140 4 7 500 200 4 7 714 280 4 7 1000In Invention Example 24 (for PPP-32) a very good and pronouncedprint-out image is observed, i.e., the exposed areas were dark blue asopposed to the light-green background color of the non-exposed areas. InComparative Example 8 (for PPP-31) the IR-dye in the exposed areas arebleached resulting in a weak visual image.

Print Results

After exposure, the plates were mounted on an ABDick 360 printing pressand a print job was started using Van Son 167 ink (trademark of VAN SON)and Rotamatic (available from UNIGRAFICA GmbH) as fountain liquid. Acompressible rubber blanket was used and prints were made on 80 g paper.For both plates, positive printed images were observed.

Invention Example 25 Preparation of the Printing Plate Precursors PPP-33

Composition was prepared (pw=parts per weight; wt. %=weight percentage)by mixing the components as specified in table 12. The solution wascoated onto electrochemically roughened and anodically oxidized aluminumsheet, the surface of which had been rendered hydrophilic by treatmentwith an aqueous solution of polyvinyl phosphonic acid (oxide weight 3g/m²) and was dried for 1 minute at 120° C. (circulation oven)

TABLE 12 Composition of the Photosensitive Layer Composition (g) PPP-33KL 7177 (1) 3.875 CIR-03 0.2003 Triazine BU1549 (2) 6.0 FST426R (3)1.875 Edaplan LA411 (4) 0.3375 Dowanol PM (5) 34.87 Dry thickness (g/m²)1.50 (1) KL 7177 is a solution containing 32.4 wt. % of amethylmethacrylate/methacrylic acid copolymer (ratio 4:1 by weight; acidnumber: 110 mg KOH/g) in 2-butanone (viscosity 105 mm²/s at 25° C.) (2)Triazine BU1549 is2-[1,1′-biphenyl]-4-yl-4,6-bis(trichloromethyl)-1,3,5-triazine fromClariant (3) FST426R is a solution in 2-butanone containing 88.2 wt. %of a reaction product from 1 mole of2,2,4-trimethyl-hexamethylenediisocyanate and 2 moles ofhydroxy-ethylmethacrylate (viscosity 3.30 mm²/s at 25° C.) (4) EdaplanLA411 is a surfactant (1% solution in Dowanol PM ® trade mark of DowChemical Company) obtained from Munzing Chemie (5) Dowanol PM ispropyleneglycol monomethylether obtained from Dow Chemical

On top of the photosensitive layer a solution in water with thecomposition as defined in Table 13 was coated and was dried at 110° C.for 2 minutes. The so-formed protective overcoat had a dry thickness of2.0 g/m².

TABLE 13 Composition of Overcoat Solution Component Parts by Weight (g)partially hydrolyzed polyvinylalcohol 17.03 (degree of hydrolysis 88%,viscosity 4 mPa · s in a solution of 4 wt. % at 20° C.). partiallyhydrolyzed polyvinylalcohol 7.43 (degree of hydrolysis 88%, viscosity 8mPa · s in a solution of 4 wt. % at 20° C.). fully hydrolyzedpolyvinylalcohol 14.87 (degree of hydrolysis 98%, viscosity 6 mPa · s ina solution of 4 wt. % at 20° C.). Acticide LA1206 (1) 0.26 Metolat FC355 (2) 0.38 IRD-004 3.42 Lutensol A8 (90%) (3) 0.032 Water 982.1 (1)Acticide LA1206 is a biocide, commercially available from Thor (2)Metolat FC 355 is an ethoxylated ethylenediamine, commercially availablefrom Munzing Chemie (3) Lutensol A8 (90%) is a surface active agent,commercially available from BASF

Image Formation

After drying of the overcoat layer, the plates were imaged with a CreoTrendsetter IR laser (830 nm) at 275 mJ/cm². In Invention Example 25(for PPP-33) a very good and pronounced print-out image is observed,i.e., the exposed areas were dark blue as opposed to the pale greenbackground color of the non-exposed areas. This is also illustrated inTable 14 by the optical density, measured with a GretagMacbeth D19Cdensitometer, commercially available from Gretag-Macbeth A G, on theexposed and non-exposed areas, using the cyan setting (OD-cyan) and alsothe black setting (OD-black), and with the uncoated support of the plateas reference.

TABLE 14 Optical Density Values OD-cyan OD-cyan OD-black OD-blackEXAMPLE non-exposed exposed non-exposed exposed number area area areaarea Invention 0.83 1.24 0.37 0.68 Example 25

Invention Examples 26 and 27 Preparation of the Printing PlatePrecursors PPP-34 and 35

Compositions were prepared (pw=parts per weight; wt. %=weightpercentage) by mixing the components as specified in Table 15. Thesolutions were coated onto electrochemically roughened and anodicallyoxidized aluminum sheets, the surface of which had been renderedhydrophilic by treatment with an aqueous solution of polyvinylphosphonic acid (oxide weight 3 g/m²) and was dried for 1 minute at 120°C. (circulation oven)

TABLE 15 Composition of the Photosensitive Layer Composition (g) PPP-34PPP-35 KL 7177 (1) 3.750 3.750 IRD-025 0.3438 IRD-024 0.3438 TriazineBU1549 (2) 0.2063 0.2063 FST426R (3) 1.875 1.875 Edaplan LA411 (4)0.3375 0.3375 Dowanol PM (5) 36.25 36.25 Dry thickness (g/m²) 1.50 1.50(1) to (5): see table 12

On top of the photosensitive layer a solution in water with thecomposition as defined in Table 16 was coated and was dried at 110° C.for 2 minutes. The so-formed protective overcoat had a dry thickness of2.0 g/m².

TABLE 16 Composition of Overcoat Solution Component Parts by Weight (g)partially hydrolyzed polyvinylalcohol 17.03 (degree of hydrolysis 88%,viscosity 4 mPa · s in a solution of 4 wt. % at 20° C.). partiallyhydrolyzed polyvinylalcohol 7.43 (degree of hydrolysis 88%, viscosity 8mPa · s in a solution of 4 wt. % at 20° C.). fully hydrolyzedpolyvinylalcohol 14.87 (degree of hydrolysis 98%, viscosity 6 mPa · s ina solution of 4 wt. % at 20° C.). Acticide LA1206 (1) 0.26 Metolat FC355 (2) 0.38 Lutensol A8 (90%) (3) 0.032 Water 960 (1) to (3): see Table13

Image Formation

After drying of the overcoat layer, the plates were imaged with a CreoTrendsetter IR laser (830 nm) at 275 mJ/cm². In Invention Example 26(for PPP-34) and Invention Example 27 (for PPP-35) a very good andpronounced print-out image is observed, i.e., the exposed areas weredark blue as opposed to the green background color of the non-exposedareas. This is also illustrated in Table 17 by the optical density,measured with a GretagMacbeth D19C densitometer, commercially availablefrom Gretag-Macbeth A G, on the exposed and non-exposed areas, using thecyan setting (OD-cyan) and also the black setting (OD-black), and withthe uncoated support of the plate as reference.

TABLE 17 Optical Density Values OD-cyan OD-cyan OD-black OD-blackEXAMPLE non-exposed exposed non-exposed exposed number area area areaarea Invention 1.02 1.45 0.50 0.83 Example 26 Invention 0.92 1.52 0.450.94 Example 27

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1-14. (canceled)
 15. An infrared absorbing dye according to Formula I:

wherein ⁺Y¹=is represented by one of the following structures:

Y²—is represented by one of the following structures:

n is 0, 1, 2, or 3; each of p and q is 0, 1, or 2; R¹ and R² areindependently an optionally substituted hydrocarbon group, or whereintwo of the R¹, R², R^(d), or R^(a) groups together include the necessaryatoms to form a cyclic structure; at least one of the R^(d) groups isselected from the list consisting of: —(N═CR¹⁷)_(a)—NR⁵—CO—R⁴;(N═CR¹⁷)_(b)—NR⁵—SO₂—R⁶; —(N═CR¹⁷)_(c)—NR¹¹—SO—R¹²; —SO₂—NR¹⁵R¹⁶; and—S—CH₂—CR⁷(H)_(1-d)(R⁸)_(d)—NR⁹—COOR¹⁸; wherein a, b, c, and dindependently are 0 or 1; R¹⁷ is a hydrogen atom, an optionallysubstituted aliphatic hydrocarbon group, or an optionally substituted(hetero)aryl group, or wherein R¹⁷ and R⁵, R¹⁷ and R¹¹ together includethe necessary atoms to form a cyclic structure; R⁴ is —OR¹⁰, —NR¹³R¹⁴,or —CF₃; R¹⁰ is an optionally substituted (hetero)aryl group or anoptionally branched aliphatic hydrocarbon group; R¹³ and R¹⁴independently are a hydrogen atom, an optionally substituted aliphatichydrocarbon group, or an optionally substituted (hetero)aryl group, orwherein R¹³ and R¹⁴ together include the necessary atoms to form acyclic structure; R⁶ is an optionally substituted aliphatic hydrocarbongroup or an optionally substituted (hetero)aryl group, —OR¹⁰, —NR¹³R¹⁴,or —CF₃; R⁵ is a hydrogen atom, an optionally substituted aliphatichydrocarbon group, a SO₃ ⁻ group, a —COOR¹⁸ group, or an optionallysubstituted (hetero)aryl group, or wherein R⁵ together with at least oneof R¹⁰, R¹³, and R¹⁴ include the necessary atoms to form a cyclicstructure; R¹¹, R¹⁵, and R¹⁶ are independently a hydrogen atom, anoptionally substituted aliphatic hydrocarbon group, or an optionallysubstituted (hetero)aryl group; or wherein R¹⁵ and R¹⁶ together includethe necessary atoms to form a cyclic structure; R¹² is an optionallysubstituted aliphatic hydrocarbon group or an optionally substituted(hetero)aryl group; R⁷ and R⁹ independently are a hydrogen atom or anoptionally substituted aliphatic hydrocarbon group; R⁸ is —COO— or—COOR^(8′); wherein R^(8′) is a hydrogen atom, an alkali metal cation,an ammonium ion, or a mono-, di-, tri- or tetra-alkyl ammonium ion; R¹⁸is an optionally substituted (hetero)aryl group or an alpha-branchedaliphatic hydrocarbon group; R^(a) and other R^(d) groups areindependently represented by a group selected from the list consistingof a hydrogen atom, a halogen atom, —R^(e), —OR^(f), —SR^(g), and—NR^(u)R^(v); wherein R^(e), R^(f), R^(g), R^(u), and R^(v)independently are an optionally substituted aliphatic hydrocarbon groupor an optionally substituted (hetero)aryl group; and one or more counterions in order to obtain an electrically neutral molecule.
 16. The IR dyeaccording to claim 15, wherein the IR dye has the structure of FormulaII, III, or IV;

wherein Ar¹, Ar² and Ar³ are independently an optionally substitutedaromatic hydrocarbon group or an aromatic hydrocarbon group with anannulated benzene ring which is optionally substituted, W¹ and W² areindependently a sulphur atom or a —CM¹⁰M¹¹ group wherein M¹⁰ and M¹¹ areindependently an optionally substituted aliphatic hydrocarbon group oran optionally substituted (hetero)aryl group, or wherein M¹⁰ and M¹¹together comprise the necessary atoms to form a cyclic structure, M¹ andM² are independently a hydrogen atom, an optionally substitutedaliphatic hydrocarbon group or wherein M¹ and M² together comprise thenecessary atoms to form an optionally substituted cyclic structure, M³and M⁴ are independently an optionally substituted aliphatic hydrocarbongroup, M⁵, M⁶, M⁷, M⁸, M¹⁶ and M¹⁷ are independently a hydrogen atom, ahalogen atom or an optionally substituted aliphatic hydrocarbon group,W³ is a sulphur atom or a —C(A³)=C(A⁴)- group, M¹² and M¹³ areindependently an optionally substituted aliphatic hydrocarbon group oran optionally substituted (hetero)aryl group, or wherein two of the M¹²,M¹³, A² or A⁴ together comprise the necessary atoms to form at least onecyclic structure, W⁴ is a sulphur atom or a —C(A⁷)=C(A⁸)- group, A¹ toA⁸ are independently a hydrogen atom, a halogen atom, an optionallysubstituted aliphatic hydrocarbon group or an optionally substituted(hetero)aryl group, or wherein each of A¹ and A², A³ and A⁴, A⁵ and A⁶,or, A⁷ and A⁸, together comprise the necessary atoms to form a cyclicstructure, M¹⁴ and M¹⁵ are independently an optionally substitutedaliphatic hydrocarbon group or an optionally substituted (hetero)arylgroup, or wherein two of the M¹⁴, M¹⁵, A⁵ or A⁷ together comprise thenecessary atoms to form at least one cyclic structure, and M⁹ is a R^(d)group selected from the list consisting of: —(N═CR¹⁷)_(a)—-NR⁵—CO—R⁴,—(N═CR¹⁷)_(b)—NR⁵SO₂—R⁶, —(N═CR¹⁷)_(c)—NR¹¹—SO—R¹², —SO₂—NR¹⁵R¹⁶ and—S—CH₂—CR⁷(H)_(1-d)(R⁸)_(d)—NR⁹—COOR¹⁸ one or more counter ions in orderto obtain an electrically neutral molecule.
 17. The IR dye according toclaim 16, wherein M¹ and M² together include the necessary atoms to forman optionally substituted 5-membered ring.
 18. The IR dye according toclaim 16, wherein the IR dye of Formula II, III, or IV has at least oneanionic group or an acid group selected from the list consisting of—CO₂H, —CONHSO₂R^(h), —SO₂NHCOR^(i), —SO₂NHSO₂R^(j), —PO₃H₂, —OPO₃H₂,—OSO₃H, —SO₃H, or —S—SO₃H groups or their corresponding salts; andR^(h), R^(i), and R^(j) are independently an aryl or an alkyl group. 19.The IR dye according to claim 17, wherein the IR dye of Formula II, III,or IV has at least one anionic group or an acid group selected from thelist consisting of —CO₂H, —CONHSO₂R^(h), —SO₂NHCOR^(i), —SO₂NHSO₂R^(j),—PO₃H₂, —OPO₃H₂, —OSO₃H, —SO₃H, or —S—SO₃H groups or their correspondingsalts; and R^(h), R^(i), and R^(j) are independently an aryl or an alkylgroup.
 20. The IR dye according to claim 18, wherein each of thealiphatic hydrocarbon groups of M³, M⁴, or M¹² to M¹⁵ of the IR dye isterminally substituted with at least one of the anionic groups or acidgroups.
 21. The IR dye according to claim 19, wherein each of thealiphatic hydrocarbon groups of M³, M⁴, or M¹² to M¹⁵ of the IR dye isterminally substituted with at least one of the anionic groups or acidgroups.
 22. The IR dye according to claim 15, wherein the IR dye has astructure according to Formula V-a, V-b, V-c or V-d,

wherein M⁺=L^(i+), Na⁺, K⁺, NH₄ ⁺, R′R″R′″NH⁺ wherein R′, R″, R′″ areindependently a H atom, an optional substituted alkyl or aryl group; andX=halogen, sulphonate, perfluorosulphonate or arylsulphonate; R³ andR^(3′) are methyl or ethyl.
 23. A heat-sensitive imaging elementcomprising an IR dye wherein the IR dye has a structure according toclaim
 15. 24. A heat-sensitive lithographic printing plate precursorcomprising a support having a hydrophilic surface or which is providedwith a hydrophilic layer, and a coating provided thereon, wherein thecoating includes an IR dye according to claim
 15. 25. The heat-sensitiveprecursor according to claim 24, wherein the coating includes aphoto-polymerizable composition.
 26. The heat-sensitive precursoraccording to claim 24, wherein the coating includes thermoplasticpolymer particles dispersed in a hydrophilic binder.
 27. Theheat-sensitive precursor according to claim 24, wherein the coatingincludes a switchable polymer which is capable of changing a polarity ofthe surface of the coating upon IR-radiation or heating from hydrophilicto hydrophobic or from hydrophobic to hydrophilic.
 28. Theheat-sensitive precursor according to claim 24, wherein the coatingincludes a polymer which is soluble in an alkaline solution, and asolubility inhibiting compound which reduces the solubility of thecoating in the alkaline solution, and wherein, upon IR-radiation orheating, the coating has an increased solubility in the alkalinesolution.
 29. A method for making a lithographic printing platecomprising the steps of: providing the heat-sensitive lithographicprinting plate precursor according to claim 24; image-wise exposing theprecursor to IR-radiation or heat; and optionally developing the exposedprecursor.
 30. A method for making a lithographic printing platecomprising the steps of: providing the heat-sensitive lithographicprinting plate precursor according to claim 25; image-wise exposing theprecursor to IR-radiation or heat; and optionally developing the exposedprecursor.
 31. A method for making a lithographic printing platecomprising the steps of: providing the heat-sensitive lithographicprinting plate precursor according to claim 26; image-wise exposing theprecursor to IR-radiation or heat; and optionally developing the exposedprecursor.
 32. A method for making a lithographic printing platecomprising the steps of: providing the heat-sensitive lithographicprinting plate precursor according to claim 27; image-wise exposing theprecursor to IR-radiation or heat; and optionally developing the exposedprecursor.
 33. A method for making a lithographic printing platecomprising the steps of: providing the heat-sensitive lithographicprinting plate precursor according to claim 28; image-wise exposing theprecursor to IR-radiation or heat; and optionally developing the exposedprecursor.
 34. A method for making a lithographic printing platecomprising the steps of: providing the heat-sensitive lithographicprinting plate precursor according to claim 25; image-wise exposing theprecursor to IR-radiation or heat; mounting the exposed precursor on aprinting press; and developing the precursor by supplying ink and/orfountain solution to the precursor.
 35. A method for making alithographic printing plate comprising the steps of: providing theheat-sensitive lithographic printing plate precursor according to claim26; image-wise exposing the precursor to IR-radiation or heat; mountingthe exposed precursor on a printing press; and developing the precursorby supplying ink and/or fountain solution to the precursor.